A CRITICAL REVIEW OF THE ANATOLIAN GEOLOGY: A DIALECTIC …

INTRODUCTION

The stratigraphy of Anatolia is characterizedby many Paleozoic - Mesozoic sections overlyingunconformably overlying the Precambrian base-ment of the Pangea. Had there been no Alpineevents, Anatolia would present sceneries similarto the grand canyon of USA. There are manysections implying such a stratigraphy. SouthernMenderes Massif, Central Taurids (Cambrian-Miocene) and Bitlis yield examples of this stratig-raphy.

The sutures of Anatolia, based essentially onthe teachings of Brinkmann (1972) and of manyothers, has first been published by Sengun et al(1990), when the East Anatolia was suggested tobe a continental fragment, in the sense that it isnot an accretionary prism, and the Tethyan su-ture was suggested to tie to the Sevan-Akerraconsidering the Munzur-Taurus connection. The

Bursa-Antalya zone has later been designatedas the Intra-Gondwanian zone separating the Ae-gean plate from the Anatolian. This has been themost important revision on the sutures ofAnatolia.

The Tethyan frames, based essentially on theAtlantic Ocean data (Smith, 1971; Pitmann andTalwani, 1972 and Dewey et al., 1973), agree onthe theory that slivers of continental crust haverifted off northern Gondwana and drifted north tocollide with Eurasia (Stocklin, 1974, 1977; Ada-mia et al., 1977; Biju-Duval et al., 1977 and Der-court et al., 1986). The essence of this theory isapplicable also to the Anatolian segment of theTethyan belt in agreement and in liaison with theneighbouring areas (Stocklin, 1977 and Biju-Duval et al., 1977). The post-Liassic part of theevolutionary frame presented in this paper is al-most world-wide accepted.

A CRITICAL REVIEW OF THE ANATOLIAN GEOLOGY: A DIALECTIC TO SUTURESAND EVOLUTION OF THE ANATOLIAN TETHYS AND NEOTETHYS

Metin ÞENGÜN*

ABSTRACT.- A progressively improving hypothesis of evolution for the Anatolian Tethys and Neotethys will bepresented in this paper. The Tethyan, the Western (Bursa-Ýzmir-Antalya zone) and the southern Neotethyansutures will be substantiated after a discussion on the controversial aspects of the Anatolian geology. The initia-tion of the Tethys in Cambrian is supported on the basis of continous Palaeozoic sedimentation on north-facingGondwanian and south-facing Eurasian platforms. A thin continental sliver, the Apula-Anatolia, started to rift offnorthern Gondwana in the Early Triassic coevally with the onset of the northward Tethyan subduction. The mar-ginal ophiolites have obducted onto the Pontian active margin by the Middle Triassic as the consequence of thedextral rotation of Western Pontides. The compressional and dilatational fields have shifted oceanward due to arecess (?) of the subduction zone. The positive area covering most of the central and northern Sakarya has col-lapsed progressively and has been onlapped peripherically from the Liassic onwards. The Anatolian microconti-nent detached off Africa in the Upper Triassic-Liassic and drifted northward during the Jurassic and theCretaceous and collided incipiently with the Eurasian margin (Pontides) in the Upper Cretaceous. Unsubductedpockets of ocean floor have closed with consequent syn-collisional magmas in the Paleogene. The Salt Lakepocket, the East Anatolia and the Western Neotethys, the Intra-Gondwanian rift separating the Anatolia fromApulia-Greece, have survived until the Late Miocene.

Key words: Controversial aspects of the Anatolian geology; sutures of Anatolia; geological and geophysical con-straints; possible evolutionary frames; geologic evolution.

* The author unfortunately has passed away during the processing of the manuscript. The corrections and thechanges were carried out by his colleagues and very close friends who know him very well in a way to be con-sistent with his thoughts and beliefs . The author has completed his work span in MTA and performed invalu-able scientific performances in Geology. We remember him with a great mercy.

Mineral Res. Exp., Bull., 133, 1-29, 2006

Metin ÞENGÜN

On the other hand, the very diverse disputeson Anatolia will be discussed in this papertowards a plate tectonic model for the AnatolianTethys/Neotethys by mounting the discussed evi-dence on a basic and generalised frame of evo-lution. Unfortunately, what has been publishedabout the Anatolian geology is an intermingledand living bundle of imaginary hypotheses.Many quests have naturally arisen on the exist-ing theories/interpretations with consequentialrevisions and corrections as the field evidencehas progressed. Some of the controversies willbe discussed in this paper, hoping that a step willbe taken towards the final solutions.

A CRITICAL REVIEW OF MAJOR DISPUTES

The Eastern Mediterranean and the Tethyandisputes will be discussed below with some ofthe entailed arguments, which are crucially relat-ed to Tethyan/Neotethyan evolution of Anatolia.

The Eastern Mediterranean dispute

The main controversial issues have been theage of rifting of the Eastern Mediterranean and

the origin of 'Antalya nappes'. It has been sug-gested that the Eastern Mediterranean has notrifted until the Cretaceous and the 'Antalya nap-pes' have originated from northern Anatolia, thenorthern margin of the Gondwanaland (Ricou etal., 1974-1986; Dercourt et al., 1986). This theo-ry is in debate with the theory of Triassic age ofrifting of the Eastern Mediterranean and southernorigin of Antalya nappes (Robertson and Wood-cock, 1981; Robertson and Dixon, 1984; Pois-son, 1984; Özgül, 1984 and Yýlmaz, 1984). St-ructural and stratigraphic evidence is in full com-pliance with the Early Triassic rifting and theauthor is in full agreement with those who defendthe Antalya complex to consist of Tertiary imbri-cations of the continental margin and the margin-al Neotethyan ocean floor of the Antalya region.

The Anatolia fragment must have rifted offnorthern Gondwana harmoniously with what hasbeen suggested by Stocklin (1974, 1977) andBiju-Duval et al (1977) respectively for CentralIran and Apulia-Greece. It is tied to Central Iranin the east and bounded by the Menderes massifin the west while the Karaburun-Biga must be theeastern margin of Apulia-Greece. The Western

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Figure 1- Sutures of Anatolia (Revised after Þengün et al,1990).

Neotethys or the Bursa-Ýzmir-Antalya zone com-prises Triassic sediments as the base of a Meso-zoic sequence (the Antalya nappes). This showsthat the rifting is not directional but scattered innorthern Gondwana with the implication that initi-ation of rifting of Apulia and Anatolia is contem-paraneous although the detachment may be not.The rifting of the southern Neotethys has beenascribed to the drag caused by the northwarddiving Tethys (Robertson, 1990). This is agree-able and seems an effective factor in addition tothe essential control, rifting of the Atlantic.

The Antalya complex is the prototype of An-talya nappes and is well studied (Lefevre, 1968;Robertson and Woodcock, 1981; Poisson, 1984;Özgül, 1984 and Yýlmaz, 1984). Unfortunately,rifting margins of northern Gondwana have alsobeen defined as Antalya nappes as in the casesof the central and eastern Alanya massif, Biga,Karaburun-Ýzmir or Kütahya. The Mesozoic fi-ning-upward sediments of these areas are un-conformable/gradational on the Palaeozoic, withthe implication that a continental crust basesthem. The Palaeozoic sequences of the riftingmargins are similar to that elsewhere in theTaurids, while the Mesozoic sections reflectunstable conditions caused by the neighbouringrifting. The Lower Palaeozoic is represented byan alternating series of carbonates, quartzitesand pelites while thick carbonate sections areencountered in the Devonian and the Permo-Carboniferous. There is generally a sharp facieschange into turbiditic sediments in Schytianalong rifting margins. The Antalya nappes arecharacterised by a flyschoid sequence with inter-mittent basic volcanism during Carnian-Norian(Antalya and Karaburun) followed by deep ma-rine carbonates of Jurassic-Cretaceous age.

The allochtoneity of the Antalya nappes, inc-luding the rifting margins of the Neotethys, hasalmost been unquestioned and the discussionshave been focused on where they had comefrom (Brunn et al., 1975). Southern origins havebeen defended for Alanya and Antalya (Poisson,

1984; Özgül, 1984) disputing the northern origindefended by Ricou et al., (1974-1986).

The Alanya debate

Özgül's (1976) structural analysis, a widelyaccepted tectonic model for the Taurids, defendsallochtonous entities or tectono-stratigraphic u-nits that are piled up on one another. These areGeyikdað, Bozkýr, Bolkardað, Antalya, Alanyaand Aladað. The structural setting of the Alanyawith respect to the Antalya unit will be discussedbelow for description of the ongoing dispute.Evidence will be presented to defend that theAntalya and Alanya units are in situ, versusfloatation of Alanya on an also allochtonousAntalya (Ricou et al., 1974; Özgül, 1976-1984;Ulu, 1983). A northeast section (Figure 2) fromDemirtaþ to the flyschcorridore (the Antalya unit)is described below essentially through theauthor's window with occasional reference to anddiscussion on the views of the contraveners.

Carbonates and slates, in the southern part ofthe section (Point 1 in Figure 2), dated respecti-vely as Cambrian and Ordovician (Özturk et al.,1995), constitute the overturned southern flank ofan asymetric anticline in the core of which gar-netiferous micaschists are exposed. The micas-chist has the following generalised paragenesis:Quartz+Muscovite+Garnet+Mg-chlorite+Albite/Oligoclase±Biotite. The physical conditions of al-mandine-amphibolite facies or of the mediumgrade (Winkler, 1974) implied by this paragene-sis are certainly incomparable with those of theoverlying incipiently deformed Palaeozoic rocksthat are exposed in rest of the section. TheCambrian carbonates have been locally shearedout in the northern flank, whereupon the garnetif-erous micaschist has come into tectonic contactwith the Ordovician-Silurian shales/slates. Thesheared contact zone between the micaschistand the overlying shales/slates displays a confor-mable fabric. However, the compositional chan-ge is very sharp, implying the impossibility of agradation in physical conditions of metamor-

ANATOLIAN SUTURE BELTS 3

Metin ÞENGÜN

phism. Therefore, an unconformity, in analogy toother Precambrian basements, seems to be theplausible relation.

The micaschist comprises lenses of amphibo-lites consisting essentially of pyroxene, amphi-bole and pyrope-almandine rich garnets. Blockformation is presumably due to the extremeincompetency of the micaschist. The amphibolitelenses have been interpreted as alpine eclogiteson the basis of the omphacitic (very close todiopsitic augite) composition (Okay and Özgül,1982) of the pyroxene. However, lenses with theassemblage of pyroxene+amphibole+almandineare well known and commonly encountered inthe Precambrian basements of Anatolia. Theyare also peculiar to Eurasian-Gondwanian Pre-cambrian basements in Europe as well as Africaor Arabia. These rocks are hydrous and have ahigh plagioclase-amphibole content, which is not

acceptable for eclogites. It is customary to definethese rocks as garnetiferous amphibolites.

However, the more important question iswhether or not the micaschist-amphibolite as-semblage is part of a basement underlying un-conformably a Palaeozoic-Mesozoic sequence.An analysis is attempted below on the relationsof pseudo-tectonic units, Alanya and Antalya, insearch of an answer to this question.

A vertical fault on the Demirtaþ road juxtapos-es the Triassic sandstones of the Antalya unit tothe Lower Palaeozoic rocks of the Alanya unit ofÖzgül (1976), a few km northeast of the micas-chists (point 2 in Figure 2). This fault has beenevaluated as the base of the Alanya unit of Özgül(1976), while it is a normal (vertical) fault of minorimportance to the author. The downthrow is notmore than a few meters. The Ordovician shales-

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Figure 2- A tentative sketch map and cross-section from Alanya to the Hadim nappe via the flysch corridore, toshow the relations between the tectonic (?) units of Alanya and Antalya. The westernmost Alanya, untilthe town of Gündoðmuþ, is the stratigraphicand the structural continuation of the Antalya complex, thepresent morphology of the Antalya gulf being the result of the 30° sinistral rotation of the Beydaðlarý(Robertson, 1990) and dextral rotation (?) of the eastern side.

ANATOLIAN SUTURE BELTS

slates appear randomly below the soil cover onthe downthrown side. The Triassic sandstones ofthe tectonic window lie horizontally on theserocks. These observations show that the Triassicsandstones overlie the Lower Palaeozoic slatesunconformably and this fault causes the juxtapo-sition of these rock units. The base of this sectioncomprises Cambro-Ordovician rocks (Öztürk etal., 1995), overlying the garnetiferous mica-schists. These cannot be included in the Antalyaunit, which is devoid of Palaeozoic sediments bydefinition. This section is not significantly differ-ent from the Geyikdað or Aladað unit of Özgül(1976) except that it has a Precambrian base.The deformations are restricted to Alpine shearzones. The Palaeozoic sequence is almost thesame as that of any other location in the Taurids.

The Alanya unit of Özgül (1976) has beensuggested to float on an entirely undeformedsequence. The Upper Permian pelmicrites, withwell-preserved fossils, display a broad andsymetric anticline in the suggested tectonic win-dow, with a clear gradation to variegated shalesof Schytian age as the base of a continousMesozoic sequence (Ulu, 1983). This sequenceis unconformable on Ordovician shales/slatesthat sit on the garnetiferous micaschists. Thedescribed sequence proves very clearly that theAntalya unit of the pseudo-tectonic window has acontinental character.

The northern boundary of the tectonic windowis a thrust fault dipping 30 to the north on theroad exposure. This fault dies out on both sidesaccording to observations of the author and isone of the several northward dipping ecailles ofthe Alanya. It dissects a gradational and conti-nous Permian- Lower-Middle Triassic sequence.The Alanya massif (Palaeozoic rocks with incipi-ent deformation) is overlain by the Triassic rocksof the tectonic window a few kms north of thenorthern boundary of the tectonic window. Thisoutcrop has been defended as evidence againstthe allochtonous nature of this sequence. How-ever, the contraveners interpreted it (Özgül,

1984) as an upthrow of Antalya onto the Alanyaversus the earliest interpretation of a sedimen-tary contact (Blumenthal, 1951). The deformationin this region is almost nil and hardly differentfrom that of the tectonic window. Furthermore,there are other exposures (Öztürk et al., 1995),Middle and Upper Triassic in age, sitting on Pa-laeozoic sediments in the northwesternmostAlanya, incompatible with the stratigraphy de-fended (Özgül, 1976 -1984) for the Alanya unit.

The examination of the northern boundary ofthe Alanya massif (Figure 2) yields crucial evi-dence. The Alanya massif has been thrusted im-bricately onto the Cretaceous-Eocene section ofthe flysch corridore or the Antalya unit of Özgül(1976) in the westernmost segment. The bound-ary is a thrust trending E-W until the town ofGündoðmuþ where it assumes a southwardtrend. Although the southward turn has beenrecognised informally by some, the boundarybetween the Alanya and the flysch corridore con-tinues to be accepted as the previously definedEW trending thrust. This boundary continuesfrom Gündoðmuþ eastward, to the author, with-out any thrusting but with discontinuous normalfaults with the northern blocks downthrown (Point3 in Figure 2). There is Upper Paleocene-deposi-tion throughout the eastern half of the northernboundary covering mutually the Alanya, theflysch corridore and the northern zone of De-mirtaþlý (1984). On the other hand, the western-most part of Alanya, as the eastern continuationof the Antalya Complex, has been thrusted imbri-cately onto the flysch corridore after Eocene.There has been no objection to this evidence,which shows very clearly that the central/easternpart of the Alanya is in situation. Being moreelaborate, it proves that:

1- The Alanya could not have been transpor-ted relative to the flysch corridore (Antalya unit)after Paleocene with Paleocene-Eocene clasticson its back, because the cover is mutual on theAlanya and the northern zone (Geyikdað unit).

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Metin ÞENGÜN

2- The Antalya nappes of the tectonic windowcannot be connected to that of the flysch corri-dore because of emplacement ages of pre andpost Upper Paleocene. This means that the Alan-ya needs to have been emplaced after the youn-gest sedimentation of the pseudo-tectonic win-dow, which is Upper Cretaceous in age (Ulu,1983), and prior to the Upper Paleocene deposi-tion. However, there is no evidence, a reason oran implication for a pre-Upper Paleocene event.

3- The absence of the Antalya unit betweenthe Alanya and the northern zone of Demirtaþlý(1984) and the gradation between the Alanyaand the Geyikdað tectonic units is indicative of anormal stratigraphic order rather than piled uptectonic units.

On a rough asessment of the temporal dimen-sion, the argument presented above excludes allbut the Uppermost Cretaceous-Upper Paleoceneinterval for a possible allochtony. However, theUpper Cretaceous cap in northernmost part ofcentral Alanya brings on a further constraint. Theconglomeratic base is horizontal and has beeninterpreted as a faulted contact (Ulu, 1983), whileit is a sedimentary one to the author. Whateverthe relation is, the presence of Upper Cretaceoussedimentation on Alanya indicates dilatation inthe Upper Cretaceous, quite incompatible withan overthrusting phenomenon. In fact, it marksthe onset of a grabenization (the flysch corri-dore). This location needs to be observed by athird party for the crucial conclusion that theAlanya cannot be transported after the UpperCretaceous, implying there is no interval fortransportation.

The idea of allochtonous Alanya is a hyphoth-esis asserted in search of an answer to howAlanya has been metamorphosed. A chronologi-cal sequence of the theories for Alpine metamor-phism of the Alanya massif is listed below to con-tribute to a further understanding of the Alanyadebate. The Alanya unit is:

1- An allochtonous entity that has been defor-med at northernmost Gondwana (Ricou et al.,1974).

2- An autochtonous asemblage with an alpineHP/LT deformation of the westernmost part (Þen-gün et. al. 1978).

3- An allochtonous assemblage of southernorigin, a deformed active continental margin withglucophane bearing assemblages (Okay and Öz-gül, 1982)

4- An allochtonous entity metamorphosed inthe island arc setting in the vicinity of Cyprus(Özgül, 1984).

5- An autochtonous mass in the central/east-ern segment while the western part, suffering aHP/LT alpine metamorphism, is the eastern partof the Antalya nappes (Figure 2).

The author's perspective for the Alpine meta-morphism is as follows. The Central Taurids, ro-tated dextrally by the Ecemis fault (Figure 1),compressed the marginal ophiolites in the vicini-ty of the Antalya gulf during the Paleogene. Thishas resulted in northward thrusting of the margin-al ophiolites of the Antalya gulf onto theBeydaðlarý and the westernmost Alanya. Thenorthern margin of the Antalya basin has beenimbricated with these thrust sheets in the arealying west of the town of Gündoðmuþ. On theother hand, there is a gradual twist, from Gün-doðmuþ eastward, of north vergent folds to thesouth vergent of the central and eastern Alanya.This observation implies a dextral torsion thathas been caused by the southward push of thewestern block of the Ecemis fault versus thenorthward thrusting of the western Alanya. It hasfolded and twisted the central Alanya so as toexpose the Precambrian basement in the vicinityof the Alanya town. The post-Eocene obductionof ophiolites and imbricate northward thrusting ofwesternmost Alanya have caused a very-lowgrade (sensu Winkler, 1974) metamorphism

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(blue schist facies) in that region. The contempo-rary deformation appears as northward dippingshear zones in the central and eastern Alanya.The convertion of the Palaeozoic pelites to slatesor phyllites are restricted to these shear zones.The alpine deformation on the Precambrianmicaschists appears as imprints of shear planes,which intersect mutually the Ordovician shales/slates. They appear as quartz-chlorite veins,which have a discordant relation to the Pre-cambrian paragenesis in thin sections of the mi-caschists. Pseudomorphs of chlorite after garnetmay also be considered as a frequently encoun-tered symptom of the alpine imprint.

The westernmost Alanya is tectonically andstratigraphically similar to the western side of theAntalya gulf. On the other hand, the central andeastern part of the Alanya is not different strati-graphically from the other tectonic units of Özgül(1976), which differ from one another by facieschanges and deformational variations only. Inconclusion, the central and eastern Alanya is insituation.

The alpine metamorphism of the Tauric belt isin close relation to rotational processes. Therelated strike-slip faults of the western Tauridshave not yet been recognised formally althoughmany scientists have declared that rotationshave played a very important role (personal com-munication with Dr. Robert Hall) in the structuralevolution and the present configuration of theNeotethyan ophiolites. They have created dilata-tion on one side while causing thrusting anddeformation on the other, resulting in appearanceof deformed and undeformed rocks side by sidethroughout the western Taurids.

THE TETHYAN DISPUTE

The evidence that the Upper Jurassic con-glomerates of Central Pontides contain serpenti-nite pebbles (Yýlmaz, 1979) triggered anothermajor dispute, a very complex one, on the evolu-tion of the Anatolian Tethys. The oceanic crust

has been dated unquestionably as Jurassic-Cretaceous in the Ankara-Ilgaz part of the Ýzmir-Ankara zone of Brinkmann (1972) and the adja-cent Triassic deformation has been covered byan undeformed sedimentary wedge of Liassic-Lutetian age along the southern Sakarya.Þengör and Yýlmaz (1981) have challenged theprevious models accordingly, with a radically dif-ferent plate tectonic model. They have presumeda two-stranded Tethys, the consecutive Palaeo-tethys and the Neotethys, with respective posi-tions of north and south of the Cimmerian tec-tonites. This model has been a benchmark in thehistory of plate tectonic interpretations for theAnatolian segment. It complies with the followingchain of reasoning made up with evaluation oftoday's knowledge.

1- There is an ocean along the Ankara-Ilgazzone, the rift separating the Western and EasternPontides, during the Jurassic-Cretaceous, and acontinous Mesozoic on the Gondwanian side inthe vicinity of Kütahya (Özcan et al., 1988), imp-lying the Palaeotethys to be located north of theCimmerian tectonites.

2- The Palaeotethys must have had a south-ward polarity for compliance with the Paleo-tethyan / Neotethyan evolution of Pontides.

3- When the southward polarity is accepted,the Pontian magmatism, being on the passivemargin, cannot be of the IA type. Thus, it has tobe ascribed to crustal thickening or some otherphenomenon.

4- A passive margin cannot suture with entireundeformation so that the European margin hasto consist of allochtonous entities to hide thePaleotethyan suture and comply with the crustalthickening.

The kinematics of evolution, as suggested byÞengör and Yýlmaz (1981), seems readily accep-table once one accepts the need or the obligationfor an ocean responsible for the Cimmerian de-

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Metin ÞENGÜN

formation. However, there has to be somethingwrong with this chain, which is, to the author, thenegligence of the possibility of marginal ophioliteobduction onto the active European margin with-out a continent-to-continent collision. The modelof Þengör and Yýlmaz (1981 was confronted withseveral other objections immediately (Bergoug-nan and Fourquin, 1982; Robertson and Dixon,1984) and after the work in the 1980's (Üþümez-soy, 1987).

Þengün et al., (1990) have objected by claim-ing that the northern branch of Neotethys is actu-ally the Tethys and has been consumed underthe Pontides through northward subduction. Themarginal ophiolites have been emplaced onto theactive margin in the initial stage of convergence,in Lower-Middle Triassic. The obduction is ascri-bed to the dextral rotation of Western Pontidesduring the Lower-Middle Triassic, as implied bythe marked southward offset of the EasternSakarya. This is in analogy with what has hap-pened in the case of the Antalya gulf. Theobducted ophiolites on both sides of the Antalyagulf are covered by unfolded sediments ofMiocene age, although the Eastern Mediter-ranean has pockets of unsubducted ocean floorsouth of Cyprus and Crete, implying that ophio-lites can be emplaced onto active margins beforecompletion of a continent-to-continent collision.A recessed (?) subduction, ascribed to a highrate of Tethyan convergence, occurred in theEarly Upper Triassic. The consequence of therecess has been dilatation on the upwarped con-tinental margin, when an island arc was set up inthe Upper Triassic. The upwarped continentalmargin or the island arc has become a progres-sively collapsing terrain, being onlapped by theTethys and the Black Sea.

On the other hand, most of the tectonic mod-els dealing with the pre-Liassic events acceptgenerally the closure of a marginal ocean toexplain the Cimmerian deformation. One of theseis the idea of closure of a local (Küre) marginal

European basin in the Early Mesozoic (Ustaömerand Robertson, 1992). The latest proposal (Gön-cüoðlu, et al, 2000), with an evolutionary sce-nario similar to that of Þengör and Yýlmaz (1981),defends a Triassic-Tertiary Ýzmir-Ankara Oceangeographically coincident with the Ýzmir-Ankarazone of Brinkmann (1972) instead of the Liassicnorthern Neotethys.

GEOLOGICAL AND GEOPHYSICAL CON-STRAINTS OF THE TETHYAN EVOLUTION

The dialectic analysis of the Tethyan conver-gence can only be complete after assesment ofthe existing evidence and arguments.

1- There is no crustal thickening in the Sa-karya fragment.

The Bougeur anomaly maps of Turkey, pre-pared by the geophysical department of theTurkish Geological Survey (MTA), display con-tours that run very smoothly through the entireWestern Pontides. A uniform continental crust,35 km. thick, has been estimated for westernPontides. This evidence justifies the objections(Bergougnan and Fourquin, 1982) to the hypoth-esis of Liassic crustal thickening (Þengör et al.,1980).

2- Sakarya fragment has a Palaeozoic sed-imentation unconformably capped by thesouth-facing Karakaya formation.

Paleozoic sedimentation in northern seg-ments (Ýstanbul and Zonguldak Palaeozoic) ofWestern Pontides is of the shallow marine typecovered by the Kocaeli Triassic comprising ofcontinental and shallow marine sediments. TheCarboniferous is only partly shallow marine innorthern Western Pontides, and generally con-sists of coal bearing sediments. Red sandstones,possibly fluviatile, were mapped to represent thePermian of this region. Towards the south, thePermo-Carboniferous rocks are represented byshallow marine carbonates and are the grada-

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tional base of the south facing Triassic flysch.Thus, the Permo-Carboniferous of Western Pon-tides, or the Eurasian Karakaya formation issouth-facing. There are two sections one bet-ween Daday and Azdavay (Þengün et al, 1990)and the other in the Ankara region where theKarakaya is unconformable on the Palaeozoic(Figure 3).

3- Detachment of the Anatolian fragmentwas not complete prior to the Liassic.

Rifting in northern Gondwana started in LatePermian/Early Triassic on the basis of strati-graphic and sedimentologic evidence. However,the Anatolian microcontinent has been suggest-ed (Þengün, 1993) to detach off Africa not in theEarly Triassic but in the Late Triassic- Liassic.Because, time is needed for crustal thinning andthe related Carnian-Norian volcanism must haveoccurred prior to the detachment. This sugges-tion is to point out that there is no discrepancybetween the kinematic (Westphall et al., 1986)and the structural/ stratigraphic/sequential evi-dence.

4- The allochtoneity of the Pontian Palaeo-zoic is hyphothetical.

Ýstanbul Palaeozoic is the term commonlyused to denote a vaguely defined area essential-ly on the eastern side of the Ýstanbul strait innorthwesternmost Western Pontides. The activemargin of the Tethys in Thrace is the Strandjhamassif, the domed westward continuity of theÝstanbul Palaeozoic (Caðlayan and Yurtsever,1999). The suggestion of the allochteneity of the'Ýstanbul Palaeozoic' is a means of elimination ofthe contradiction that this domain is of Europeanorigin but located south of the Palaeotethyansuture of Þengör and Yýlmaz (1981). The sug-gested thrust (Þengör et al., 1980, 1984) andstrike-slip faults, which revise the former theoriesof thrusting (Okay et al., 1994), have been nei-ther substantiated nor there has been a hintpointing to a locality where the thrusting or thestrike-slip faulting has been observed. The only

location that may be considered as the base ofthe proposed nappes comprising the Palaeozoicrocks of the northern Western Pontides is theDevrekani charriage, which is 400 and 600 kmrespectively to the Ýstanbul Palaeozoic and theStrandjha. Furthermore, the age of this charriageis not Liassic as suggested by Yýlmaz (1979) andÞengör et al., (1980), but is post Upper Creta-ceous as it captures globotruncana bearing sed-iments on its front (Þengün et al., 1990). Thisoverthrust comprises of the Precambrian-Mesozoic sequence as the overriding block, cap-turing on its front, many ophiolite outcrops withunconformable Cretaceous sediments. It contin-ues not only to the Ankara region southwards,but is also continuous in the north causing forma-tion of the ridge (Zonenshain and Le Pichon,1986) that separates the Eastern and theWestern Black Sea.

5- Northern branch of Neotethys has beenannulled.

Northern strand of Neotethys of Þengör andYýlmaz (1981) has never existed. Instead, thereexisted an ocean, the Ýzmir-Ankara zone ofBrinkmann (1972) whose suture is of the Tethysfrom Ilgaz to the city of Bursa where it splits toÝzmir as the Western Neotethys (Figure 1) andcontinues to the Vardar zone via the Sea ofMarmara. The Tethyan suture connnects to theSevan Akerra through the Eastern Pontides-Eastern Anatolia boundary. The following aresome of the reasons for annulment of the north-ern Neotethys.

There is a continuous Lower Triassic-Cretaceous fining upward sequence, Kütahya,south of the northern strand of Neotethys (Özcanet al., 1988). This evidence shows on its own thatthis suture belongs to an ocean that existed atleast for the entire Mesozoic (Þengün, 1990;Göncüoðlu, et al., 1994), in fact, to the Palaeo-zoic- Mesozoic Tethys on the basis of north fac-ing Gondwanian and south facing Eurasian Pa-laeozoic platforms.

9

Metin ÞENGÜN10

Figure 3- Figure to show various features of the eastern-Central Pontides. Cross-sections AB and CD illustratethe routes along which the type sections of the Karakaya formations ,can be seen. The deformationaugments towards the south where a type of melange is encountered representing the shallow seg-ments of shear zones. The type sections are oversimplified to emphasise the fact that rocks and strati-graphic relations are well preserved because of being carried on the back of the uppermost slice.


There is extensive geochemical research, alldefending the Triassic-Jurassic (?) magmatismof the Pontides to be of the island arc type(Boztuð et al., 1985; Kazmin et al., 1986 and To-kel, 1992).

On the northern side of the suture, namely inthe Sakarya fragment, there is a post-tectonicsedimentation unconformable on the Cimmeriantectonites. It generally starts in Liassic as a finingupward sequence (Þengün, 1992). The sequen-ce is continuous from the Liassic to the upper-most Cretaceous in the Eskiþehir (Bingöl andNeugebauer, 1992) and Ankara regions. On theother hand, a post-tectonic wedge in the range ofPortlandian-Lutetian is well established in theCentral Pontides. North-facing character of thelatter is readily recognised on the Boyabat-Sinopand Devrekani-Çatalzeytin roads. The UpperJurassic-Lutetian sections are almost identicalwith their counterparts in the sections startingwith the Liassic. This sedimentary wedge is veryprobably related to the Tethyan onlap in thesouth while it is definitely a Black Sea sequencenorth of the positive area. The evidence is indica-tive of a transgression diminishing the positivearea centering the Sakarya fragment. Therehave been small islands that have not beentransgressed until the end of Eocene as indicat-ed by local columnar sections.

The Liassic-Lutetian sediments cover uncon-formably the Palaeozoic rocks and the Karakayaformation, the latter being restricted to the south-ern belt juxtaposed to the Tethyan (or the pseu-do-Neotethyan) suture. The Karakaya formation,Carboniferous-Triassic in age, bears a geneticrelation to this suture, which cannot be of theLiassic Neotethys, but the Carboniferous-Tri-assic Tethys. The regressive Triassic of thenorthern Tethyan margin versus the fining up-ward Mesozoic sequence of the southern is notcompatible with a Liassic extensional basin, buta Mesozoic active margin in the north and a pas-sive one in the south.

6- The Mesozoic magmatism of the WesternPontides is of the island arc type and is Up-per Triassic in age.

The Upper Triassic basic magmatism of Cent-ral Pontides have been differentiated to yield agranitic magma, followed by high silica differenti-ates. The basic magmatism is displayed veryneatly in Central Pontides hosting the granitic.The granitic bodies display extremely wideaphanitic perypheries, implying that they havebeen very shallow seated and the country rockhas been very cold. There are many granitebatholithes (comprising basic rocks as the host)in Central Pontides dissecting mutually ophio-lites, the Palaeozoic sediments and the Kara-kaya formation. Boztuð et al (1985) state that thebasic and the granitic magmas of this regionbelong to the same magmatic suit. The author,agreeing with this statement, suggests further-more that the granitic magma is the differentialproduct of the basic. The suggestion is based onthe basic rocks being the host for the granitic andthe striking resemblance of the pleochroism ofthe hornblend phenocrystals of the diorites andthose of the granitic rocks, crucially implying thecontinuity of crystallisation of hornblend of a spe-cific composition. Further petrochemical investi-gations should, hopefully, check up the sugges-tion. This proposal has the crucial implication thatthe basic and granitic magmatism are of thesame age.

On the other hand, the radiometric dating of165±3 my for the granite (Yýlmaz, 1979) cannotbe proven wrong for the Central Pontides on thebasis of direct evidence. Nevertheless, no gran-ite dyke has been reported to dissect any sectionof Liassic age. Secondly, the sedimentary wedgecovering the Karakaya complex is Upper Ju-rassic-Lutetian in age in the northern CentralPontides, with full stratigraphic correlation of thesection with those of the Ankara and Eskiþehirregions (Saner, 1980; Bingöl and Neugebauer,1992). In other words, the Liassic-Cretaceoussedimentation of these regions are tied to the

11

Metin ÞENGÜN

Central Pontides, showing very clearly that thiswedge covers the magmatism and the Triassicdeformation. In conclusion, the granitic magma-tism has to be Upper Triassic in age to be com-patible with the stratigraphic constraints, and isnot post-collisional but of the island arc type inCentral Pontides on the basis of extensive geo-chemical research.

7- The Karakaya enigma

There has been an enigma on the Karakayaformation caused by the similarities between theTriassic sedimentation on Gondwanian andEurasian margins. The nomenclation (Bingöl,1968) has been applied to both (Sakarya andBiga).

The Gondwanian Karakaya is Mesozoic inage while the Eurasian is Carboniferous-LateTriassic.

The Gondwanian Triassic (Antalya nappes)grades to deep marine Jurassic-Cretaceous sed-iments while the Eurasian ends up in the UpperTriassic, being invariably regressive in the UpperTriassic section.

The Gondwanian Permian blocks are coveredand underlain by continuous layers that convergeon both ends. The strata are turbiditic with blocksof various dimensions. There is no crystallizationin Permian limestones. The fauna has Gond-wanian affinities. On the other hand, the Permianblocks north of the Tethyan suture are of the bro-ken type and partly crystallised. Block formationof the Eurasian Permo-Carboniferous in theTriassic sandstones is encountered essentially inthe shear zones.

The Triassic of the Eurasian Karakaya isrestricted to a belt adjacent to north of the Teth-yan suture and has never been deposited out-side this narrow belt. Thus, it is genetically relat-ed to the southward-located Triassic Tethys. Onthe other hand, the deposition of the Gond-

wanian sequence is scattered on northern Gond-wana and is related to dilatation of the Anatolianmicrocontinent.

There is a type section/area between Beytepeand Ýmrahor in the vicinity of Ankara. The north-ward younging section north of the deformedsuture is carried on the back of the uppermostslice (Figure 3, sections AB and CD). It compris-es of:

1- A lower Palaeozoic clayey unit exposed inthe vicinity of Eymir Lake.

2- Carboniferous-Permian limestones with aconglomeratic base.

3- High-energy clastics of Lower Triassic agegradational to Permian limestones.

4- A continous carbonate sedimentation of Ju-rassic-Cretaceous age covering these unconfor-mably.

5- Serpentinites juxtaposed to Liassic- Creta-ceous carbonates on the Eskiþehir road.

Block formation in the Eurasian margin oc-curs, to the author, mostly in shallow segments ofUpper Cretaceous-Paleocene thrusts, whichhave dragged the inter/back-arc regions towardsthe Tethyan suture. The deformation diminishesgoing away from the suture so that undisruptedsequences, with extremely rich faunas, can beseen as in the case of Permo-Carboniferousrocks in the vicinity of Ankara. The Cretaceousdeformation appears as rhythmic and southwardnarrowing shear planes. The deformations arerestricted to these shear planes so that thelithons, when fairly distant to the suture, can dis-play the previous, i.e. the Triassic deformations.In other words, the belt with intense Cretaceousdeformation grades northward, to the zone withpre-Liassic deformations showing rhythmic andprogressive northward diminishing of its Creta-ceous imprint.

12


The Karakaya formation is a marker of theEuropean margin in the Sakarya where it isunconformable on Palaeozoic sequences ofEuropean origin. It is of Gondwanian origin in theBiga-Karaburun as will be discussed in the fol-lowing item.

8- The Sakarya fragment is of Europeanorigin while the Biga is of Gondwanian.

Which continental fragment (Figure 1) be-longs to which major continent? Is there satisfac-tory evidence for the origins of the Sakarya andthe Biga? These are probably the most signifi-cant and appropriate questions that should beraised for the Anatolian segment of the Tethyanbelt. There is no direct claim based on paleonto-logic evidence that the Biga is European butimplied to be hypothetically (Okay and Tüysüz,1999). On the other hand, European origin ofSakarya (Þengün et al., 1990) receives accept-ance in the recent years. The present authorclaims on the basis of sequential evidence thatthe Sakarya is European while the Biga is ofGondwanian origin.

There is a continuous Triassic-Cretaceoussequence in the Biga peninsula (Koçyiðit andAltýner, 1990) and there are many Mesozoic fin-ing-upward sequences along the Bursa-Ýzmirzone (Akdeniz, 1985). The D'orsay group (Brunnet al., 1975; Ricou et al., 1974-1986) has definedthese as the Antalya nappes, the very typicalGondwanian facies. The Triassic sequence ofthe Biga, or the Karakaya formation of Bingöl(1968) has also been defined as the Antalyanappes. The Antalya nappes of the Karaburunpeninsula, which has been declared as Gond-wanian and juxtaposed to the Bursa-Ýzmir zone(Erdoðan, 1990), are certainly on the continua-tion of the Biga Peninsula, the Aegean and theGreece. Bursa-Ýzmir zone comprises other Lo-wer Triassic-Upper Cretaceous sequences (Ak-deniz, 1985), substantiating the designation ofthis zone as intra-Gondwanian.

The Karakaya formation sits, with a sedimen-tary contact (Þengün et al., 1990), on the Palaeo-zoic rocks of Eurasian origin in the Daday-Az-davay section of the central Pontides. The Car-boniferous of the Beytepe- Ýmrahor section of theAnkara region sits on the underlying Devonianshales also with a sedimentary contact. AnythingEuropean in any part of these sections impliesthe European character of the whole. The Eu-ropean character of the Sakarya fragment (Þen-gün et al 1990) is backed up not only sequential-ly but also paleontologically. The Liassic sedi-mentation of the Sakarya contains Europeanammonites (Alkaya, 1990) and the Eurasian ori-gin of the Zonguldak Carboniferous is well estab-lished (Kerey, 1982, Toprak, 1984). It has beenasserted (personal communication with Prof. E.Ya. Leven of Moscow University) that the Permo-Carboniferous carbonates of the Beytepe(Ankara) section (Figure 3) have a very rich Eu-rasian fauna.

Nevertheless, further investigations will hope-fully complement the sequential evidence andthe paleontologic assertion cited, to show thatthe Sakarya belongs to Europe while the Bigapeninsula to Gondwana. A consensus on the ori-gin of the Biga will resolve many of the entailingdisputes such as the Intra-Pontide Ocean.Further paleontologic and paleomagnetic workson the Permian limestones of Biga may yield evi-dence that will hopefully resolve the ongoingdebate.

9- The Intra-Pontide Ocean is hypothetical.

Okay et al (1994), Okay and Tüysüz (1999)and Göncüoglu et al. (2000) defend an E-W tren-ding intra-Pontide ocean separating the Sakaryaand northern Pontides. The author's objectionsto existence of this ocean are outlined below.

The sediments, younger than the Liassic, areundeformed on both sides of the suggested Int-ra-Pontide suture, which is mostly coincident withthe NAF.

13

The belt of Upper Cretaceous volcanicstrends perpendicular to the suggested strike-slipfaults and shows no offsets in Central Pontides.

An unbroken Pontide belt is unacceptable(Lauer et al., 1981). The abrupt end up of theIntra-Pontide ocean in the middle of the Pontidesis not only subject to objection as a concept butalso brings in the necessity to explain the east-ward ophiolite thrusts onto the Kirsehir massif,which are connected to ophiolites of the Daday.

The Portlandian-Lutetian sedimentary wedgecovers the paleo-lineament that causes the offsetof the Daday-Devrekani massif with respect tothe Ilgaz in northern Central Pontides. On theother hand, the Liassic-Lutetian wedge has start-ed to transgress the northern Pontides in Port-landian as a result of the progressive collapse ofthe Western Pontides. Therefore, the lineament,by which the Western Pontides has been dis-placed southwards relative to the EasternPontides, must have died out by Portlandian.This interpretation is backed up by the hardlydetectable offset between the Elekdag (Figure.3)and the westward continuation (Karadere ophio-lites) separated by the Arac-Boyabat graben.

Yýlmaz et al (1994) have suggested an UpperCretaceous closure of the Intra-Pontide Oceanversus the Paleogene collision of Okay and Tuy-suz (1999). However, the lack of deformation onthe Mesozoic rocks on both sides of the sutureseems to be an important drawback for either ofthese theories. The active margin may be unde-formed because of being carried on the back ofthrust sheets. However, non-deformation along apassive margin is unacceptable

THE SUTURES OF ANATOLIA

THE NEOTETHYAN SUTURE

The northern branch of the Neotethys(Þengör and Yýlmaz, 1981) seems to be annulled(Þengün et al, 1990; Okay et al, 1994), leaving

one Neotethyan suture in Anatolia as shown inFigure 1, the southern and the western zonesbeing connected (?) through the Eastern Medi-terranean. The western branch possibly con-nects to the northern Antalya basin of Robertson(1990) and the loop north of Karaburun towardsthe Vardar zone is theoretical. The loop is theo-retically undeletable to maintain the distinctionbetween the Tethyan and Ýntra-Pontian sutures.In other words, elimination of this loop or accept-ance of the Biga as Gondwanian would meancoincidence of the Tethyan and the Intra-Pontiansutures. However, the suture cannot passthrough north, in disagreement with Okay andTüysüz (1999), of the broadly folded Mesozoicsediments of the Gondwanian Karaburun (Er-doðan, 1990), but passes through the southwestof this peninsula (Gökten et al., 2001) where theophiolites have been ultramylonitised due toimbrication with the continental rocks of theMenderes massif (personal observation with Dr.N. Konak and. Mr. A. Caðlayan). This means thatthis suture is in between the Karaburun and theMenderes, both of which being of an undoubtedGondwanian origin. The Menderes massif, thedomed continuation of the Taurids, has a Pa-laeozoic-Mesozoic cover (Çaglayan et al, 1980)in the southern segment of the Izmir-Ankarazone. The sections exclusively display the se-quential and palaeontological characteristics ofthe Tauric facies. This evidence backs up theconnection of this zone to the Antalya basin. Thesuture and the Lycien nappes, the latter beingpresumably related to the compressive field gen-erated in relation to closure of this zone, haveprobably been subject to post-collisional config-ureuration by strike-slip faults.

The southern Neotethyan suture passesthrough the immediate north of the Pütürge(Yazgan, 1984) and the Bitlis massifs, and notthrough the zone known as the Bitlis suture (Hall,1976) or the southern branch of Neotethys ofÞengör and Yýlmaz (1981), which is referred toas the Maden-Cungus foredeep in this text. Thisassertion is based on detailed regional geologi-

Metin ÞENGÜN14

cal mapping of eastern Bitlis (Caglayan et al.,1984) and the Puturge massifs (Yazgan, 1984).

The following information is a summary of theevidence that show Bitlis to be in situ and theuplifted passive margin of the southern Neo-tethys.

The Mesozoic sequence of the southeasternBitlis (Caðlayan et al., 1983), exactly the sameas that of the border folds, not only shows thatBitlis and the border folds were on the samenorth-facing Mesozoic platform of Gondwana butalso proves that Bitlis is in situ. It also implies thatthere has been no rifting along the Bitlis suture ofHall (1976) until the end of the Mesozoic.

Southern branch of Neotethys or the Bitlissuture of Hall (1976) is juxtaposed on both sidesby undeformed rocks. The Bitlis/Puturge block isrepresented by a Precambrian basement cappedunconformably by incipiently deformed Palaeo-zoic-Mesozoic (Yýlmaz, 1971) and there is noquest for the undeformed nature of the borderfolds (Þengün, 1990). Can the northern blockhave a sheared Precambrian basement so that asubduction zone is sealed? No, because there isnowhere any sign of such a deformation. Is aTriassic rifting possible south of Bitlis? There isno sign of changing sedimentologic parametersneither in Permian limestones, nor in the Triassicsedimentation, which is exactly the same asthose of the pseudo-suture and the border folds.This means that there has been a Permo-Tri-assic platform extending from northern Bitlis/Pütürge to the Arabian platform.

The intensity of alpine deformation, un-dressed of folding, diminishes towards the south,showing that the suture lies in the north.

Bitlis massif is the uplifted passive margin ofthe Neotethys on the basis of the island-arc set-ting in its immediate north (Yazgan and Chessex,1991) and the southward obducted Gevas ophi-olite (Caðlayan et al., 1984).

The overall geophysical evidence shows thatthere has been a collage between the East Ana-tolia and the Bitlis/Puturge in the Upper Creta-ceous. The ophiolites have been obducted ontothe passive margin (Bitlis/Puturge) from the Ce-nomanian onwards (Yazgan, 1984; Yazgan andChessex, 1991). There is a consensus that theobducted ophiolites imbricated with the crustalrocks of Bitlis glide gravitationally into this fore-deep. This is a crucial support to the dilatationalregime implied by the sedimentation between theUpper Cretaceous and Miocene.

The closure of the pockets of unsubductedocean floor has resulted in formation of fore-deeps south of Bitlis and Puturge. This processis reflected in the sedimentation and the mag-matic activity. The initiation of the extensionalMaden-Cungus trough is indicated by convertionof carbonate sedimentation of the southeasternBitlis to gradational high-energy clastics ofCampanian- Maastrichtian age. The dilatationand sedimentation is continous including theMiocene along this trough.

The rotations generate dilatation causing par-tial melting in the uppermantle-lower crust. A syn-collisional magmatism, the Maden formation,forms and is expelled through diabase dikesalong NNE trending paleo-transtensional faultsthat spread the lavas as flows intercalated incoeval sedimentation in the EW trending troughsextending along both extremities of the Bitlismassif.

The thrusting of Bitlis onto this graben tookplace in the Late Miocene after the collagebetween the East Anatolia/ Pontides and comple-tion of the Neotethyan closure, with the aid of theNNE push of the Arabian platform (McKenzie,1972). Detailed mapping has shown that the Bit-lis head-thrust of Altýnlý (1963), which borders themassif in the south, is not a single plane but com-prises of many unlinked thrusts (Ozkaya, 1982).It is possible to cross from the Eastern Bitlis tothe Dodan anticline of the border folds without


any thrusting. Thus, the division of the northernArabian platform into tectonic slices of Bitlis, oro-genic flysch and the border folds is a false andunsubstantiated hypothesis, but is currentlyaccepted.

Yazgan (1984) has described the magmaticand stratigraphic relations to show that the Neo-tethys also lied not in the south but the immedi-ate north of the Pütürge massif.

West of the Puturge massif, the suture has asouthward displacement of 105 kilometers(Freund et al., 1970) by the Dead Sea transformso that it passes through the north of well-knownpockets of unsubducted ocean floor south ofCyprus and Crete in the Eastern Mediterranean.There has been Neotethyan acretions to theTaurids as in the case of Antalya Complex (Ro-bertson and Woodcock, 1981; Yýlmaz, 1984;Poisson 1984 and Özgül, (1984). It is possiblethat the Northern Antalya basin may be tied tothe Ecemis lineament. However, this issue is leftout because of the author's inadequate know-ledge of this region.

The reason for the misinterpretation (Þengün,1993) about the Bursa-Ýzmir segment of the Ýz-mir-Ankara zone of Brinkmann (1972) was theacceptance of the Biga as Gondwanian followedby the consequential false reasoning that thiszone could have been a foredeep only. Manyhave considered ophiolites of the Menderesmassif as transported tectonites originating fromthe north, although the imbrication with theMenderes massif is suggestive of a suture. TheSSW trend of the Ýzmir-Bursa zone also backs upa suture. The author has realized on the basis ofthe preceding thoughts that this zone is not aTethyan but an Intra-Gondwanian Neotethyan riftseparating the Anatolian microcontinent fromApulia-Greece. It seems that this rift has to con-nect to the Northern Antalya Basin of Robertson(1990) via the west of the Lycien nappes ofsouthwest Anatolia.

THE TETHYAN SUTURE

A Cretaceous-Paleogene (?) Tethyan suturebetween Bursa and the coastal areas of the Seaof Marmara substantiates itself by the ophioliteslivers that show the same high pressure/lowtemperature metamorphism and the same defor-mational geometry as the eastern Sakarya. TheTethyan suture is theoretically connected to theVardar zone through the Sea of Marmara also onthe basis of the Biga being Gondwanian and theSakarya of European origin. The Tethyan suturecoincides with the northern strand of theNeotethys of Þengör and Yýlmaz (1981) betweenBursa and Ankara. It is also well marked in thesegment bounding the Eastern Pontides and theEast Anatolia and is characterised by imbricatesouthward thrusting (Yýlmaz, 1985). The Mio-cene blocks in emplaced ophiolites juxtaposed tothe Tethyan suture shows that the suturing of theTethys in East Anatolia has not been completeduntil the Late Miocene.

A wide belt of ophiolites thrusted onto theKirsehir massif marks the Tethyan (+Neoteth-yan) suture between Ankara and Ilgaz. This ophi-olitic slice is connected to that of the Daday mas-sif via the Arac - Boyabat graben. The suturinghas caused uplift of the passive margin, theKirsehir massif with an intense multistage Alpinedeformation with southeastward diminishinggrade of metamorphism (Erkan, 1975; Seymen,1982 and Tolluoðlu, 1987).

A DISCUSSION ON POSSIBLE SCENARIOSOF PRE-LIASSIC GEOLOGIC EVOLUTION

The post-Liassic evolution of Dercourt et. al.(1986) is mostly agreeable except the evolutionof the Eastern Mediterranean. Most of the tecton-ic models accept that closure of a marginal basinis unavoidable to explain the Triassic deforma-tion. The possibilities and selected past hypho-theses on the issue will be examined briefly.

I. The Paleotethys dives Southward underGondwana comprising Southern Sakarya and

Metin ÞENGÜN16

the Biga. Northern Neotethys is a Marginal(Back-Arc) Gondwanian Basin (Þengör andYýlmaz, 1981).

The key point has been that there must havebeen a collage responsible for the Cimmerianorogen in the Sakarya fragment, as there is aJurassic-Cretaceous ocean floor south of theCimmerian tectonites in the Sakarya fragment.However, the following geological and geophysi-cal constraints are not consistent with thehyphothesis of Þengör and Yýlmaz (1981).

1- The gap between the Taurids and the Pon-tides is more than 4 000 kms in the Liassic(Westphall, et al, 1986). Thus, a collision by M.Jurassic is almost impossible.

2- The geophysical evidence is suggestive fora uniform crust with a thickness of about 35 kmsin Pontides, thinning smoothly towards the BlackSea, justifying the objection of Bergougnan andFourquin (1982) to the theory of crustal thicken-ing.

3- The Liassic-Dogger piling of the Palaeo-zoic rocks of the northern Pontides is false alsobecause of the post-Upper Cretaceous age ofthrust faults. These have a widening spacinggoing away from the Tethyan sutuýre. They cap-ture many bodies of serpentinites with Cretace-ous caps in the Sakarya fragment and are cer-tainly related to the Tethyan suturing.

4- There is concrete evidence for non-exis-tence of the northern strand of Neotethys of Þen-gör and Yýlmaz (1981).

5- The ascription of the Upper Triassic (Ju-rassic?) magmatism to crustal thickening is ex-clusively denied by extensive geochemical re-search (Boztuð et al., 1985, Kazmin et al., 1986and Tokel, 1992), all defending the IA type.

Göncüoðlu et al. (2000) have proposed a sim-ilar scenario representing the latest of the de-

fenders of the possibility. The pre-Liassic evolu-tion is the same as that of Þengör and Yýlmaz(1981) except that the Ýzmir-Ankara ocean or thenorthern strand of Neotethys has opened in theLower Triassic. The following criticism is addi-tional to the ones enumerated above.

1- The Mesozoic dilatation of the southernmargin of the Ýzmir-Ankara ocean is not compat-ible with the coeval compressive state of thenorthern margin in the Triassic. Known const-raints back up a passive margin in the south andan active one in the north.

2- The theory has to explain how the Mesozo-ic fining upward sequences of the Bursa-Ýzmirzone is replaced on the eastern continuation, theSakarya, by a weakly deformed Carboniferous-Triassic overlain by the undeformed Liassic-Lutetian sedimentary wedge. Can these sequen-ces belong to the same continental margin? Thecrucial constraint is the Gondwanian and Eu-rasian origins respectively for the Biga and Sa-karya. Both of these fragments have to be of thesame origin for consistency of this model. Bothhave to be of either Gondwanian origin or Eura-sian, as the marginal Karakaya Ocean couldhave not possibly extended in both of the majormainlands. Therefore this model has to defendthe Gondwanian character of the Biga and south-ern Sakarya for consistency. However, theEuropean character of the Sakarya is well estab-lished.

3- The Ýzmir-Ankara ocean, separating theMenderes-Taurid block from the Sakarya, cannotopen in the Triassic, because this means that theGondwana and Eurasia had formed a single con-tinental mass in the Triassic, unless a very thincontinental fragment of Gondwanian origin isseparated from the European by an ocean atleast 4000 km wide.

II. There has been a Southward diving the Eu-ropean Marginal Basin Responsible for theTriassic deformation (Ustaömer and Ro-bert-son, 1992).


The objections to this possibility is summa-rised as follows.

1. There is no direct evidence showing that aEurasian sliver has collided with Europe by theLiassic.

2. A marginal European basin can be possibleonly if it is in the range of Carboniferous-UpperTriassic, coeval with the Karakaya formation,because the Karakaya formation is uncon-formable on the European Palaeozoic se-quences (Þengün et al., 1990). This implies thata southward polarity (Ustaömer and Robertson,1992) is unavoidable with the chain conse-quence that the granites of Central Pontides,being located north of any European marginalbasin, has to be ascribed to crustal thickening.The theories with a southward polarity are notcompatible not only with the incipient deforma-tion of the Palaeozoic sequences underlying theKarakaya formation of northern Pontides, but arein contradiction with the extensive geochemicalresearch (Boztug et al., 1985; Kazmin et al.,1986 and Tokel, 1992), exclusively suggesting anisland arc origin for the granitic magmatism.

3. Another objection to a southward divingEuropean basin would be that the Cimmeriandeformation intensifies southward showing thecause of deformation is in the south of the accre-tionary prism.

4. A gradation exists through northward wide-ning tectonic slices in the Western Pontides (Sa-karya).

5. The Karakaya formation of the Sakaryafragment is European and is juxtaposed continu-ously to the northern (the Tethyan) suture, imply-ing that such a marginal basin has to be coinci-dent with the Tethys.

6. Along the Izmir-Bursa zone, there is a con-tinuous fining-upward Mesozoic sequence,which has been defended as the GondwanianKarakaya, also known as the Antalya nappes. On

the other hand, the Sakarya fragment is charac-terised by the European Karakaya formation ofCarboniferous-Triassic age. Thus, these seg-ments are genetically different and are not partsof a single continuous margin.

III. The European (Intra-Pontian) Marginal Ba-sin dives Northward.

A European marginal basin (in a model anal-ogous to that of Adamia et al. (1977), noting thatthe marginal basin in the Caucasus correspondsto the Black Sea) diving north may be consideredpossible, only if the Carboniferous-Upper Trias-sic sedimentation unconformable on Europeanrocks is false or ignored. In that case, the Kureophiolite needs to have been emplaced on theactive margin by rotationary processes of thecontinental margin so that it can be intruded bythe island arc magmatism. The mechanismwould not be significantly different from thatdefended in this paper for both the EasternMediterranean and the Tethys. Existence of finitepieces of continental crust that have beendeformed into an unrecognisable state by theTriassic/Cretaceous events cannot be provenwrong. However, such a theory has to place themarginal basin in the middle of the accretionaryprism, leaving a remarkably narrow strip ofsouthern margin, which has left no fingerprintsbehind.

IV. There is no Marginal Intra-Pontian Basin.

The Triassic deformation is caused by themarginal ophiolite obduction onto the activeEuropean margin without a continent-to-conti-nent collision. This is the possibility preferred, soit will be described and defended below.

GEOLOGIC EVOLUTION

PRECAMBRIAN

The Precambrian basement is exposed in se-veral locations in Turkey. Alanya, Menderes, Kýr-þehir, Bitlis and Puturge are well-known Gond-

Metin ÞENGÜN18

wanian massifs with Precambrian basements.There are several other exposures in northernPontides underlying unconformably uniform andincipiently deformed Palaeozoic sequences. ThePrecambrian basements comprise essentially ofamphibolites and micaschists/paragneisses me-tamorphosed in physical conditions of alman-dine-amphibolite facies. Granites have intrudedthese and have been deformed by the Alpineuplift only. Palaeozoic- Mesozoic sedimentscover these unconformably in the Central Taurids(Özgül, 1976-1984). The westward narrowinggulf of the Pangea (the Tethys) seems to haveinitiated with the beginning of the Palaeozoic Era(Figure 4).

PALEOZOIC

There has been immense stratigraphic re-search since the late 1960's in Central andWestern Taurids. Detailed mapping in the follow-ing years resulted in new disputes about thestructure. However, there is almost full agree-ment on the Palaeozoic stratigraphy of theTaurids. The continental (coal bearing) to shallowmarine Permo-Carboniferous sequence of theAlanya massif and other Lower Palaeozoic sedi-ments of Western Taurids grade to continuousPalaeozoic marine sedimentation northwards,implying a north-facing Tauric platform (Blumen-thal, 1951; Özgül, 1984; Demirtaþlý, 1984).

The stratigraphy and sedimentologic parame-ters of the Palaeozoic fining upward sedimenta-tion in northern Pontides are suggestive of dilata-tion during the Lower Palaeozoic, converted tocompression during the Permo-Carboniferous.There is a continuous Palaeozoic sequence inthe Karadere region west of Daday. If a south-facing morphology is acceptable for theKarakaya formation, the continuous Palaeozoicimplies that there has been an ocean south ofthese sequences during the entire Palaeozoicera. The Carboniferous and older rocks of thenorthern Pontides were subject to southwardonlap of the Black Sea, the Central Pontides

remaining as a positive area until the LateJurassic. It was not transgressed completely untilthe Late Cretaceous or even Eocene.

The stratigraphic, sedimentologic and mor-phologic evidence for the formation of the Tethyscan be complemented with the Atlantic Oceandata for the conclusion that the Tethys had awidth of roughly 5000 kms in the vicinity ofAnatolia at the end of Permian as suggested byWestphall et. al., (1986).

MESOZOIC-PALEOGENE

TRIASSIC

There have been marked facies changes inthe Taurids with initiation of rifting in northernGondwana. Permian limestone deposition hasbeen converted, along the Neotethyan margins,to high-energy deposition represented essential-ly by turbiditic sequences with Permian limestoneolistolithes. The crustal attenuation initiated basiceruptions during the Carnian-Norian. The cessa-tion of this volcanism presumably marks theonset of ocean-floor spreading in Neotethyanrifts. Facies changes between the rifting marginsand the positive areas result in juxtaposition ofdeep and shallow marine environments.

The replacement of carbonate deposition byhigh-energy clastics in southern Pontides is sug-gestive of a Triassic onset of northward subduc-tion of the Tethys. However, the author questionsthe deepening environment even for the begin-ning of the Triassic period with the consequentquest on the indispensability of a subduction inthe Early Triassic. The Triassic sedimentation ofthe Karakaya formation is represented by high-energy clastics with rare interbeds of limestonesyielding fossils of Lower, Middle and UpperTriassic age. The section in the Ankara region(Figure 3) represents the proximal part of theEurasian continental slope. The Lower Triassicsegment comprises blocks of Permian lime-stones. The Upper Cretaceous thrusting as


Metin ÞENGÜN20

Figure 4- A tentative and unscaled chain of evolutionary cross sections from the Eastern Mediterranean to theBlack Sea.

described in the preceeding sections has brokenup the Permian limestones resulting in blocks ina Lower Triassic matrix in the Permian-Triassicboundaries. The Triassic sequence of the Kureregion sits on the abyssal clays covering thesheeted dykes and is the representative of themarginal ocean floor. It continues as a regressivesequence comprising carbonate interbeds thatyield Lower, Middle and Upper Triassic fossils.There are small serpentinite wedges in the medi-al part of the section with sheared bottoms andsedimentary tops, implying that the emplacementis coeval with the deposition.

JURASSIC

The assesment of the kinematic evidence(Westphall et al., 1986) implies that the westernand central Taurids seem to be moving withAfrica until the Early Jurassic. Therefore, thesuggestion of a Liassic age of detachment isplausible and is compatible with the geophysicalconstraints (Figure 5).

The Gondwanian sedimentation comprisesessentially of deep marine carbonates in subsid-ing troughs such as Izmir-Bursa zone, Kutahyatrough and Karaburun. There are sharp facieschanges perpendicular to the axes of these sub-siding troughs with gradations to relatively shal-lower environments and onlaps onto the positiveareas. The sedimentologic record is indicative ofcontinuous dilatation during the entire Mesozoicin the Anatolian microcontinent. Rifting has oc-curred in the Eastern Mediterranean south andnorth of Cyprus/Crete, the northern strand possi-bly extending as the Northern Antalya Basin con-necting to the Ýzmir-Bursa zone and the Ecemis(?) lineament in the east.

The Liassic initiation of deposition on thePontian arc seems to have occurred in areas ofearlier collapse along the southern coast of theisland arc. The northern part of the WesternPontide block has persisted as a positive areabetween the Late Carboniferous and the UpperCretaceous. The Central Pontides have been


Figure 5- A sketch map to show the relative positions of the main continental and oceanic domains in the Upper Triassic - Liassic.

transgressed in Portlandian-Berriasien in liasionwith the progressive collapse. The time of onlapis Albian in the Daday region while it is UpperCretaceous in areas that are fairly distant fromthe suture, such as the Ýstanbul and ZonguldakPalaeozoic. The times of onlap on two sides ofthe same hill are Berriasien and Campanian inthe Elekdag region where the basal columnarsection is the same, displaying the same rocksequence. It must be emphasised again, that theUpper Cretaceous transgressions are not relatedto initiation of rifting of the Western Black Sea,but to onlap of the existing. Thus, the WesternBlack Sea must have started to rift before theJurassic, very probably in the Early Triassic to bein consistency with the hypothetical dextral rota-tion of Western Pontides.

The Liassic deposition from Ankara region toBursa, in Western Pontides, is suggestive of thesubduction to trend parallel to the Tethyansuture. It is not possible to say that there hasbeen coeval subduction in the Ankara-Ilgaz zoneduring the Liassic, and ocean floor spreadingcould have been dominant, particularly in thesouthern segment of this zone, conformably withthe possible dextral rotation of Western Pontides.

CRETACEOUS-NEOGENE

The Cretaceous was a period of rapid driftingof the Anatolian microcontinent towards the Pon-tides. The deposition has continued in the exten-sional basins of the Anatolian microcontinent andthe back-arc basin of northern Pontides. Slicingof the active margin must have continuedthroughout the period resulting in a HP/LT meta-morphism along the suture. Ophiolite obductiononto the passive margins, the Kýrþehir andMenderes massifs, must have started towardsthe end of the Cretaceous period. It is observedthat the slicing is imbricate and the lithons widensouthward. It is suggested to have progressedtowards the south, the earlier slices having beencarried on the back of the following. The thrust-ing has resulted in uplift of the passive margin

with consequent gravitational gliding towards theforedeeps that are suggested to form by rotation-ary processes of the collisional period. Therewere presumably pockets of unsubductedoceanic crust after the collision (Figure 6), as thecontinental fragments are not expected to fit likejigsaw puzzles. The closure of these pocketsmust have been fulfilled with the aid of strike-slipfaulting with the consequence of compressionand dilatation, the latter being responsible forcreation of syn-collisional magmas of essentiallyPaleogene age. The author disagrees with thetheory that crustal thickening may be the causeof partial melting of the upper mantle/lower crust.Because, pressure is hydrostatic in depth andrigid displacements are not possible. Marine sed-imentation stops invariably by the end of Lutetianalong the Tethyan suture in Western and CentralAnatolia.

Suturing along the East Anatolia-EasternPontides has not been completed before LateMiocene. The Western Neotethys, or the BursaAntalya basin, has sutured by the Miocene asindicated by the multistage compressive defor-mation between Early Eocene- Late Miocene(Gökten et al., 2001), although most of this zonehas collided by the Late Eocene. But the imbrica-tion of the suture zone has continued until theMiocene. The sedimentation is continuous inc-luding Miocene in the vicinity of the Salt Lake. Itseems that there could have been an unsubduct-ed pocket of ocean floor there, which has closedwith the aid of NW trending strike-slip faults cre-ating an immense Tertiary magmatism NW ofAnkara (Galatya volcanics).

The northward movement of the Arabian plate(McKenzie, 1972) put a brake on rifting of theMaden-Cungus foredeep, continuing so that theBitlis have been pushed onto this basin followingthe collision between Eastern Pontides and EastAnatolia during the Miocene. The compressionhas continued to cause uplift and crustal thicken-ing of East Anatolia and formation of new platemargins such as the E-W trending dextral North

Metin ÞENGÜN22

Anatolian Fault (NAF) and the NNE-SSW sinis-tral Ecemis, followed by the NE-SW sinistral EastAnatolian (EAF), to push the western part ofTurkey onto the ocean floor south of Cyprus andCrete. It seems that the East Anatolian fault andseveral other sinistral faults en echelon with theDead Sea transform enable the push of westernAnatolia onto the Eastern Mediterranean so thatthe Ecemiþ Fault can be inactive. However,many scientists have questioned this inactivity.

The Anatolian plate escapes west not onlybecause of the northward push of the Arabianplate (McKenzie, 1972) but also the southwest-ern drag of the Aegean back-arc basin of theHellenic trench. Otherwise, the movement alongthe NAF would have died out as the Marmaraand the Aegean region had squeezed up.Nevertheless, the North Anatolian tear has oc-curred because the Pontide plate (The Eurasian)is rigid and stable, implying the southern block tobe mobile with respect to a stationary northernblock. This is the crucial point on which a deduc-tive process can be started as to locate the areaof dilatation on the North Anatolian Fault (NAF)so that a guess can be projected for future earth-

quakes, which will theoretically migrate east-ward. There cannot be a strike-slip fault parallelto the northern coast of the Marmara, for a tech-nical reason, which is the principle that such astrike slip fault has to join a plate margin. Thus,the threat will be from the NAF. The period oftime for a new earthquake of the same magni-tude along the Marmara segment is not less than150 my on consideration of the 1-5m displace-ment in the recent earthquakes and on the as-sumption of a slip rate of 1.5 (Kasapoðlu, 1984)to 2.5 cm/year.

DISCUSSION AND CONCLUSION

The Tethyan suture is characterised by aHP/LT metamorphism of the active margin andimbrication of ophiolites with the continental crustin the passive margin. A section from the BlackSea to the northern Menderes comprises of veryweakly deformed Lower Palaeozoic sedimentsunconformably capped by the south-facingKarakaya formation. This formation grades intoan unrecognizable state towards the suture mar-ked by a fairly wide sliver of ultrabasic rocks ob-ducted onto the passive margin. The passivemargin displays ecailling with a widening spacing


Figure 6- A sketch map showing unsubducted pockets of oceanic crust during theUpper Cretaceous.

away from the suture. Concrete field and exten-sive paleontologic evidence back up the Gond-wanian origin of the passive margin, the Taurid-Menderes and the Biga. The Eurasian origin ofthe Western Pontides is also well established.Origins of these continental fragments locate theTethyan suture coinciding with that of Brinkmann(1972) between Ankara and Bursa. The basicfeatures of the evolutionary frame may be sum-marised as:

a) The basic evidence for the evolutionaryframe is certainly the geophysical.

b) Sutures are not long distance thrusts, butare rotating systems that are not much longerthan 500 kms as in the case of Western Pon-tides.

c) The Ankara Ilgaz Black Sea line needs fur-ther attention, in the sense that separation ofEastern and Western Pontides is far from beingthoroughly understood.

This paper comprises of not only substantialevidence but also assertions based on theauthor's field observations. Nevertheless, the fol-lowing evidence is independent of the author'sperspective.

1- There is a post tectonic sedimentary wed-ge of Liassic Lutetian age, covering most of theSa-karya fragment with the implication of dilata-tion from Liassic onwards (Saner, 1980: Bingöland Neugebauer, 1992; Þengün, 1992a).

2- The Karakaya formation lying adjacent tothe Tethyan suture in the Sakarya is European bynot only the sequential evidence (Þengün et al,1990) but also the paleontological (Alkaya,1990).

3- The sequential and paleontologic evidence(Akdeniz, 1985; Erdoðan. 1990) shows that theBursa- Ýzmir segment of the Ýzmir-Ankara zone(Brinkmann, 1972) is intra-Gondwanian.

4- The overthrust planes of the Sakarya run-ning paralel to the Tethyan suture are of post-Cretaceous age (Þengün et. al.1990).

THE FIELD EVIDENCE WITH REGARD TOSUTURES

Southern branch of Neotethys lied not in thesouth, but immediate north of the Bitlis/Pütürgemassifs (Yazgan, 1984; Çaðlayan et al, 1984).

1- There is a continuous Mesozoic sequenceexactly the same as the border folds in easternBitlis (Çaðlayan et. al, 1984).

2- Bitlis suture of Hall (1976) is undeformedon both sides.

Northern branch of Neotethys has neverexisted. The Neotethyan suture coincides mostlywith that of the Tethys (Palaeotethys). The Bur-sa-Ýzmir zone, presumably extending to northernAntalya basin and emplacing ophiolites ontosouthwestern Anatolia (Lycien nappes), is here-by proposed as an intra-Gondwanian ocean. Ithas started to rift not in Liassic but in EarlyTriassic.

Concrete evidence is presented showing thatthe Intra -Pontide Ocean is also a pseudo-suture.

1- There are flat-lying Mesozoic sequenceson both sides of this suture.

2- The controlling strike-slip faulting suggest-ed by Okay et. al, (1994) is unsubstantiated.

3- The deformation coincides with that of theNorth Anatolian fault zone

OUTLINE OF THE GEOLOGIC EVOLUTIONOF THE ANATOLIAN SEGMENT OFTETHYS/NEOTETHYS

1- Initiation of the formation of the Tethys atthe end of Precambrian.

Metin ÞENGÜN24

2- Initiation of rifting in the Anatolian segmentof northern Gondwana and onset of northwardTethyan subduction in Early Triassic.

3- Obduction of marginal ophiolites onto thePontian active margin as the consequence of thedextral rotation of Western Pontides duringLower and Middle Triassic.

4- Recess of the subduction zone and initia-tion of the Pontian arc in Early Upper Triassic.

5- Detachment of the Anatolian microconti-nent from Africa in Upper Triassic-Liassic.

6- Northward drift of the Anatolian microconti-nent during Jurassic and Cretaceous.

7- Ophiolite obduction onto the passive mar-gin and the incipient collision of the ApuliaGreece with the Strandjha in the Upper Cre-taceous.

8- Incipient collision of western Anatolia withWestern Pontides in the uppermost Cretaceous-Paleogene.

9- Onset of rotations to close unsubductedpockets of ocean floor, coeval formation of fore-deeps and formation of syn-collisonal magmas inPaleogene.

10- Closure of the Salt Lake pocket, collisionof the Anatolian microplate with the Aegean andcollision of East Anatolia with the EasternPontides in Miocene (?).

11- Formation of the plate boundaries, theNAF and the EAF in Late Miocene.

The scenario presented in this paper willhopefully progress in future through questioningof the various other aspects of the evolutionaryhistory of Anatolia.

ACKNOWLEDGEMENTS

The author is indebted to Mr. M. A. Çaðlayanand Dr. E. Yazgan for discussion on variousissues. We are thankful to M. Atilla Çaðlayan,Mustafa Sevin and halil Keskin who correctedand rewieved the article after the author's death,consistent with his last will from them, before hedied.

The manuscript received on May 29, 2006

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INTRODUCTION

The study area, situated in 80 km east ofEskiþehir province, northwest of Sivrihisar, isshown on the 1/25.000 scaled Eskiþehir Ý-26 c4map sheet (Figure 1).

Regional geology was explored by Romieux(1942), Weingart (1954), Kulaksýz (1981), andGözler et al. (1996). However, there is not anyknown study related with mineralogy, geochem-istry and origin of emerald and accociated miner-als originated from Sivrihisar locality famous forgemstones market and recorded at historicaltimes.

If world beryllium occurrences are taken intoconsiderations in general, they seem to formmostly in schists, nepheline syenites, phonolitesand pegmatites within ophiolite belts. Based onthese informations and carrying the wholeparameters, Sivrihisar region seems to be a suit-able locality to be considered carefully for thisresearch.

MATERIAL AND METHOD

29 clastic and 29 rock samples were collect-ed along creek valleys cutting metamorphics,ophiolites and pegmatites, complying with theprinciples of geochemical prospecting. Transpa-rent and opaque minerals collected from clasticsamples by using stereomicroscope are classi-fied as groups based on their color and crystalforms. Of transparent minerals, colored mineralsconsidered to be beryl were separated, andrefractive indexes of these minerals were deter-mined under polarized light with using 0.002 mmspaced immersion oils, and their optical proper-ties were also determined. In addition, theseberyl crystals were analyzed by electron micro-scope (SEM) (Zeiss Supra 50 VP). Rock sam-ples were petrographically analyzed and theirmineral constituents and textures were deter-mined. Trace element analyses of 12 sampleswere performed for the presence of beryl to bedetermined with ICP-AES method at ACME lab-oratory (Canada).

PRELIMINARY APPROACH TO GENESIS OF BERYL GROUP MINERALS IN KAYMAZ,NW SÝVRÝHÝSAR, ESKÝÞEHÝR

Hülya ERKOYUN*, Rifat BOZKURT* and Selahattin KADÝR*

ABSTRACT.- Kaymaz (Sivrihisar) is located at 80 km east of the Eskiþehir. The study area consists of metamor-phites, ophiolites, phonolites and pegmatites. Beryl crystals are detected in the sediments which cut the meta-morphic units. Optical microscopic determinations show that beryl crystals have 35 µm diameter, green and palegreenish blue colours, hexagonal features, basal cleavages, no = 1.584 and ne = 1.584 refractive indexes, uni-axial (-) and euhedral hexagonal prismatic characters which was supported by scanning images (SEM). Be con-tent of phonolites between 9-31 ppm, of pegmatites between 4-17 ppm and of metamorphic units as 1 ppm weredetermined. Elements associated with beryllium in phonolites with F (260-440 ppm), Ba (1088-3106 ppm), La(300 ppm), Y (16-19 ppm) content, pegmatite with F (300 ppm), W (10 ppm), Sn (5 ppm) contents and presenceof beryl crystals in the sediments cutting the metamorphic units which have tectonic relation with phonolite andpegmatite, seem to imply that formation of the beryl minerals have close releationship with these units.

Key words: Beryl, phonolite, pegmatite, metamorphite, Sivrihisar

* Eskiþehir Osmangazi Üniversitesi, Jeoloji Mühendisliði Bölümü, Meþelik, 26480, EskiþehirE-Mail: [email protected]; [email protected]; [email protected]

MTA Dergisi, 133, 31-40, 2006

Hülya ERKOYUN, Rifat BOZKURT and Selahattin KADÝR

GEOLOGICAL SETTING

The study area consists of metamorphics,Karabayýr Metaophiolites, Karakaya Granodio-rite, Höyüklü formation and Sarýkaya formation(Kulaksýz 1981). Metamorphics of Upper Creta-ceous aged units forming the basement in thestudy area include an intercalation of meta-quartzite, metapelite, marble, calcschist, metab-asite, serpentine schist and metacalcirudite(Okay, 1984; Figure 2). Tectonically overlyingKarabayýr Metaophiolites contain of metagabbro,metahornblendite, metapyroxenite, metaharzbur-gite, metaserpentine and metaperidotites. Thereare also phonolite domes intruding serpentinitealong the crack formed by a fault line which haveeffects up to penetrating depths. K-Ar age ofphonolites is given as Middle Miocene (Özgenç,1982). Karakaya Granodiorite of Upper Creta-ceous intruding ophiolites as a pluton bears apegmatitic vein with quartz, feldspar, tourmalineand pyrite. Höyüklü Formation of Miocene iscomposed of volcanogenic sandstone, grey-wacke, tuff, agglomerate and lava flows. Over-lying all these units, Sarýkaya Formation of Plio-cene begins with volcanic tuff and conglomerateat the bottom and lasts with lacustrine limestone,sandstone, claystone and marl units. This forma-tion overlays locally metaophiolites with angularunconformity (Kulaksýz, 1977). The youngest de-

posits in the study area are Quaternary alluviums(Figure 3 ).

Emerald and aquamarine were detected byoptical analyses on creek sands collected fromthe valley of Karakýz Creek cutting metamorphicsto research beryl mineralization. Phonolites wereselected as second area within the ophiolites.Pegmatitic vein within granodiorite is consideredas third area.

PETROGRAPHIC STUDIES

a- Rock Petrography

Petrographic studies present that metamor-phics seem to include garnet-glaucophaneschist, epidote-chlorite schist, garnet-lawsonite-glaucophane schist, epidotite, chlorite-lawsoniteschist and marbles, Karabayýr Metaophiolitescontain diabase, serpentinite, ophicalcite andphonolites, and Karakaya Granodiorite seems tobear a pegmatitic vein as well.

In thin sections of lepidoporphyroblastic-tex-tured garnet glaucophane schist traces of chlori-tization are present on the edges of subhedralgarnets with varying sizes between 0.25 and0.75 mm (Plate I - Figure 1). Prismatic glauco-phane crystals with varying sizes between 0.125mm and 0.5 mm have significant strong pleo-chroism. With using immersion oils, refractoryindex of glaucophane is determined asnx= 1.642, ny = 1.656 ve nz = 1.657 and it impliescrossite of glaucophane series. As well as garnetand glaucophane, there are muscovite, epidote,chlorite and quartz.

In lepidoblastic - textured epidote - chloriteschist, there are epidote as elongate crystals inthe direction of b axis, clinozoisites with bluishinterference colors, and chlorite with no alignedgroups of crystals.

In nematoporphyroblastic-textured garnet-lawsonite-glaucophane schist, glaucophane min-

32

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Figure 1- Location map.

erals have sizes between 0.2 and 0.3 mm. Law-sonite minerals varying sizes between 0.08 and0.22 mm are short prismatic crystals. There areinclusions in garnet minerals. Epidote mineralsare between 0.2 and 0.65 mm, in size.

In nematoblastic-textured epidotite, euhedralalbit crystals are found together with epidotes.The size of the calcite mineral inclusions seemto be between 0.15 and 0.3 mm. Ýn size (Plate I -Figure 2).

In nematoblastic-textured chlorite lawsoniteschist, foliated crystals of chlorites surround law-sonite and epidote minerals in bunches. Law-sonite minerals are short prismatic crystals andshow parallel extinction. Epidote minerals are0.13 mm in size and augite minerals are between0.15 and 0.3 mm in size (Plate I - Figure 3).

In marble sample enclosed in metamorphics,there are very few quartz, sericite, plagioclaseand orthoclase besides calcite. Twin glidings and

BERYL GROUP MINERALS OF SÝVRÝHÝSAR REGION 33

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bendings on these twin lamellas are observed incalcite crystals. They show symmetrical extinc-tions according to the traces of cleavages.Quartz minerals are of anhedral rounded grainsand sericite minerals are flakelike assemblages.Few plagioclase and orthoclases of Carlsbadtwinning are observed.

Ophitic-textured diabase dyke within Kara-bayýr metaophiolites contain of oligoclase, diop-site, actinolite and zeolite minerals. Diopsitesperforming uralitization were converted to partialor completely acicular actinolites. Zeolite miner-al, defined as natrolite, are found as acicular-fibrous aggregates. In serpentinite, there are an-tigorite bearing olivine remnants, and fibrous

chrysotiles. In the porphyritic-textured phonolitesample (H18), there are euhedral phenocrysts ofsanidine varying between 0.2 and 0.7 mm size,hornblende with 0.015 mm. size and leucite min-erals. Its groundmass consists of volcanic glassand rock fragments (Plate I - Figure 4). Phonolitesample numbered H28 showing typically trachyt-ic texture contains nepheline and apatite mine-rals (Plate I - Figure 5). Sieve-textured ophical-cite include twin lamellar calcite, fibrous chry-sotile and subparallel aligned antigorite crystals.

Pegmatite sample enclosed in Karakaya gra-nodiorite consists of orthoclase, biotite andquartz minerals. Some of orthoclase mineralsshow Carlsbad twinnings, some have a combina-

34

Figure 3- Generalized vertical section of the study area (modified from Kulaksýz, 1981; Okay, 1984)

BERYL GROUP MINERALS OF SÝVRÝHÝSAR REGION

tion of Carlsbad and Baveno twinnings (Plate I -Figure 6). Chloritization of biotites ranging sizesfrom 1 to 4.75 mm are seen from the edges.Quartz grains are between 0.25 and 0.5 mm insize.

b- Beryl Mineralogy

Beryl, with displaying dark green color isdefined as emerald, and displaying bluish greento blue coloration, called as aquamarine, and isberyllium aluminosilicate in reality, carrying a for-mula as Be3Al2Si6O18 .

25 green and light-green colored beryl grainsowning the largest size as 35 µm, numbered asH1 from Karakýz Creek cutting metamorphics,were defined as emerald and aquamarine basedon the analyses (Plate II - Figure 1).

Views of green crystals (grains) on a stere-omicroscope imply that they are crystallized inhexagonal systems (Plate I - Figure 2).

With using immersion oils having 0.002 dif-ferent values, refractory indexes of the grainswere found as no=1.568, ne=1.584 using (Plate IIFigure 3).

Beryl minerals, in optical studies, determinedas uniaxial (-) and existed as hexagonal prismat-ic euhedral crystals were defined as emeraldwhen green, and as aquamarine when lightbluish green varieties at polarized light in immer-sion oils. (Plate II - Figure 4). Basal cleavage(0001) is significant (Plate II - Figure 5).

Beryl crystals determined on stereomicro-scope were analyzed by SEM (Plate III - Figs 1and 2) as well. Beryl crystals are euhedralhezagonal prismatic in general. 0001 planar sec-tions of these crystals are six cornered and local-ly circular. Prismatic beryl crystals showing circu-lar and elipsoidal 0001 planar sections wereprobably derived from partial abrasion of hexag-onal prismatic crystals resulting from probabletransportation within detrital sediments.

GEOCHEMICAL ANALYSES

12 samples were taken so as to determine ifberyl is existed by performing chemical analyses,in the probable emerald promising areas. Ofthese samples, 6 samples were taken from Ka-rakýz Creek cutting metamorphics (H1-H6), onesample was taken from Kötüpýnar Creek cuttingphonolites (H18) and one sample was taken fromBüyük Creek clastics cutting pegmatites (H29).Rock samples were analyzed as metamorphics(H1), phonolites (H18 and H28), and pegmatites(H29). To compare sediments and rock samplesand if there is possibility of any rock types to bearberyllium mineralizations, both rock and sedi-ment samples were analyzed.

Samples taken from Karakýz creek (H1- H6)bear 1 ppm Be, creek sands taken from BüyükCreek (H21) cutting pegmatites contain 4 ppmBe (Chart 1). The highest Be value were deter-mined as 9 ppm on creek sands taken fromKötüpýnar Creek (H18) cutting phonolites.Related with these sediments, Be content ofKaraburunsivri phonolite sample (H18) is 31ppm, of Kocasivri phonolite (H28) is 19 ppm, ofpegmatitic rock (H29) is 17 ppm and metamor-phics (H1) bear less than 1 ppm Be. These datashow us beryl has probably been derived andenriched from alkaline phonolitic and pegmatiticrocks.

Useful indicators to determine presence ofberyl are F, Li, Rb, Cs, Sn, W, and accociatedelements are Ba, Sr, B, Sc, Y, and other rareearth elements are U, Th, Nb, Ta, P, Ti, Mo andMn (Boyle, 1974). Because of Be and Li, Rb, Cs,Sr, Ba, B, Sc, Y, Ti, Th, P, V, Nb, Ta, Cr, W, U, Mnand F are lithophile elements, they are interrela-ted (Akyol et al., 1985). Of accompanying ele-ments with beryllium, various cations of smallradius and often greater valence (U 10-22, Th 4-142, Mo 2-14, W 4-17, Nb 3-182, Sn 2-5 ppm)are called as incompatible elements. Owing toionic radius and valences, the element Exchangewith major ions in silicate minerals seem to be

35

Hülya ERKOYUN, Rifat BOZKURT and Selahattin KADÝR36

Table 1- Results of geochemical analyses of the samples taken from the study area


difficult (Krauskopf, 1979). On phonolite samples(H18,H28) values of U as 15-22, of Th as 5-142,of Nb as 9-182, of Mn as 1033-1474, of Sr as467-976, of La as 21- 64, of Ba as 1088-3106, ofAl as 8.26-10.4, of Y as 16-19, and of F, a signi-ficant indicator for determining beryl, as 440-260ppm were determined. On pegmatitic rock sam-ple (H29) higher values of W as 10, of Sn as 5,of F as 300 ppm than other rock samples supportthat beryllium occurrences on the veins andpyrometasomatic beds own a geochemical affi-nity between beryllium and W, Sn and F in parti-cular. (Warner et al., 1959).

On clastics from Karakýz Creek cutting meta-morphics, the values of Cu, Ni, Co, Mn, Ca, Cr,Mg, Sc, V, and Fe; on a garnet-glaucophane rocksample taken from the surroundings of samecreek values of Ni and Cr associated with maficvolcanic and ultramafic rocks; on garnet, glauco-phane, epidote and chlorite minerals values ofCo, Fe, Ca, and Mg are high. It is noteworthy thatthe rock sample bear less Cu, Mn, Sc and V thanclastic sample does.

On clastics from the creek cutting pegmatitePb and K got concentrated, and pegmatite sam-ple (H29) enriched in W, Sn and F, and depletedin Sr and Ba. This explains that pegmatite veinsbear wolfram, tin and fluorine beds. On sedimentsample taken from Kötüpýnar Creek cuttingKaraburunsivri phonolite, the values of Al, Na,Mo, Zn, As, Th, Sr, La, Ba, K, W, Zr, Y, and Nbseem to be considerably high. On phonolite sam-ples (H18, H28), LFSE elements (Pb, Mn, Na,Th, Sr, Ba, U, K), HFSE (Y, Nb, Zn, Ti, Zr), LREE(La), transition elements (V, Sc ), lithophile ele-ments (W, F) and other elements (As, Cu, Fe, Al)got enriched.

Beryl may include alkaline ions like Na and K,and its total alkaline content may rise up to 5-7%. Beryllium replaces Na, on the contrary, does-n't replace K. Alkaline elements remain withinhexagonal channels in the lattice structure of aberyl (Çelik ve Karakaya, 1998), so high-bery-

llium containing samples bear alkaline elementsof considerably enriched values (0.04 - 5.86 %)like Na and K. In fact, Kocasivri and Karabu-runsivri phonolitic rock samples enriched in Na,K and Al, and depleted in Ca and Mg show thatthese rocks carry alkaline character.

It is indicated that there is a slight positive cor-relation between beryllium and Nb, Mo, Sn, F,Ba, Sr, U, Th and La elements; a negative corre-lation between beryllium and Sc, P, Ti, Mn, Crand V, and no correlation between W and Y(Figure 4).

Results of chemical analyses show that apositive correlation between Be and Al may existexcept for H1 sample, and Be element enters thelattice structure of Al-bearing minerals (sanidine,leucite, nepheline, hornblende, biotite, ortho-clase). Because ionic radii and ionic valences ofBe and Al are similar, these elements are isomor-phic.

DISCUSSION

It can be referred that beryl minerals wereformed due to phonolites and pegmatites in thenorthwest of Kaymaz (Sivrihisar). Beryllium ele-ment's indicating an anomaly on phonolitic andpegmatitic units, and the determination of berylcrystals in sediments cutting metamorphic rocksrelated with these units seem to exhibit signifi-cant geochemical relationship between Be andthe rocks. According to Marshall et al. (2003),emerald occurrences are closely related with Cr( +/- V) and Be-bearing solutions in general. Theauthors state that Cr and V could be derived fromlocal mafic and ultramafic rocks during hydro-thermal alteration. At the sample of Kocasivriphonolite (H28), having a high value of V and anegative association, and a higher value of Cr inmetamorphic rocks than that of other rocks indi-cate that chromium transportation is probablyresulted from thrusting. Optically determinedberyl minerals might have been formed due to anassociation with schist minerals following the

37


metamorphism of original rock during a hydro-thermal process. Depending with upthrust, alka-line magma derived solutions were filled the fis-sures and joints of the metamorphic rocks, asresult, beryl got deposited as trace amounts.

A positive correlation between Be and Na,and also K in phonolitic and pegmatitic rocksshows that beryllium could be present in a crys-tal lattice structure of some Na and K-bearingminerals like in sanidine, nepheline, hornblende,orthoclase and apatites. Because of trace

amounts of beryllium element, beryl minerals cannot be observed in thin sections of phonolite andpegmatite rocks and are mostly determined bychemical analysis methods.

Beryllium containing solutions are products ofalkaline volcanism together with F in phonolites.Be composing between 9 and 31 ppm, and Fbetween 260 and 440 ppm, and also Be between4 and 17 ppm, and F as 300 ppm in pegmatitesshow the presence of a positive correlationbetween Be and F, and a probable relation as in

38

Figure 4- Correlation charts of elements associated with Be.


origin, between them. Where beryllium's havinghihger values, F gets high values, fluorine play areactive role separating F from a solution phase,and beryllium was facilitated to get separate inpneumatolytic and hydrotermal solutions. Be-bearing minerals form due to conditional chan-ges of the solutions like pH, pressure and tem-perature or due to decaying of complexes like[BeF4]2-, [BeF2]-, [BeF2]°, [Be(CO3)F]- ve[Be(CO3)2]2- when they interact with surroundingrocks (Gökçe, 2000). Either beryllium enters alattice structure of silicate minerals or enriches inresidual solutions during magma crystallization.Which of these happened is dependent upon thefluorine content of magma, hydrostatic pressure,alkalinity of surrounding rocks and other factors.Therefore, Be either is deposited in granitic peg-matites or is carried with fluorine and formed inhydrothermal occurrences and in greisens.Higher F value on Kýzýlcaören fluoride barite oreformed at the contact of phonolites in the studyarea shows that they are derived from the samevolcanism. Hence, beryl occurrences are associ-ated with phonolites and pegmatites in origin. It isalso reported by Preinfalk and Morteani (2002)that similar occurrences derived from anatecticpegmatites in Belmont and Capoeriana (MinasGerais, Brazil) reacted with Cr-rich ultrabasicrocks in metasomatism, Beryl occurrences in thestudy area might have been formed as a result ofmetasomatic reaction between pegmatites andCr-rich ophiolitic rocks

CONCLUSIONS

1- The presence of beryl as emerald is firstlyidentified in sediments of Kaymaz locality (NW ofSivrihisar- Eskiþehir) in Turkey by mineralogicaland geochemical studies.

2- Optical properties of beryl minerals arehexagonal prismatic euhedral crystals, green-colored varieties called emerald, bluish greenvarieties called aquamarine, basal cleavage,determined light refractory indexes no= 1.568,ne= 1.584, 1st row interference colors and uni-

axial (-). On the other hand, beryl crystals onSEM are identified as euhedral hexagonal pris-matic forms.

3- For the identification and origin of be-ryllium, Beryllium shows positive correlationswith F, Ba, Sr, U, Th, La, Nb, Sn and, W ele-ments, seem to be considerably important data.

4- Beryl minerals associated with beryllium ingeochemistry as volcanogenic hydrothermalproducts related to phonolites and pegmatites.

ACKNOWLEDGMENTS

This paper is revealed from M. Sc. Thesisstudy of the first author conducted by the super-vising the second and third authors. The authorthanks to Prof. Dr. Taner Ünlü (AÜ), AssociateProf. Dr. Sönmez Sayýlý (AÜ), Dr. Neþat Konakand Dr. Eþref Atabey (MTA) with valuable criticsin revision of this paper.

The manuscript received February 10, 2006

REFERENCES

Akçay, M. 2002. Jeokimya temel kavramlar veuygulamaya aktarýmlarý. KTÜ yayýnlarý,genel yayýn no: 204, Fakülte Yayýn No. 60,506s.

Akyol, A., Ýnan, K. and Suner, F. 1985. Jeokimyayagiriþ. ÝTÜ Kütüphanesi Sayý 1308, 666s.

Boyle, R.W. 1974. Elemental association in mineraldeposits and indicator elements of interest ingeochemical prospecting. Ener-gy, Mines andResources Canada, Geological Survey Paper74-45, 40s.

Çelik, M. and Karakaya, N. 1998. Sistematik mineralo-ji. Selçuk Üniversitesi, 434s.

Gökçe, A. 2000. Maden yataklarý. Cumhuriyet Üniver-sitesi Yayýnlarý no: 85, 335s.

39


Gözler, M.Z., Cevher, F., Ergül, E. and Asutay, H.J.1996. Orta Sakarya ve güneyinin jeolojisi. Ma-den Tetkik Arama Genel Müdürlüðü Report No:9973, 87s. Ankara (unpublished).

Krauskopf, K.B. 1979. Introduction to geochemistry.McGraw Hill Book Company. 617 s.

Kulaksýz, S. 1977. Sivrihisar kuzeybatý yöresinin jeolo-jisi. Hacettepe Üniversitesi, Doktora tezi. 200 s.

,1981. Sivrihisar kuzeybatý yöresinin jeolojisi.H.Ü. Yerbilimleri Dergisi, 8, 103-124.

Marshall, D., Groat, L., Giuliani, G., Murphy, D., Mat-tey, D., Ercit, TS., Wise, MA., Wengzynowski,W. and Eaton, WD. 2003. Pressure, tempera-ture and fluid conditions during emerald preci-pitation, southeastern Yukon, Canada: fluid inc-lusion and isotope evidence. Chemical Geo-logy, 194, (1-3), 187-199.

Okay, A.I. 1984. Kuzeybatý Anadolu'da yer alan meta-morfik kuþaklar. Ketin Sempozyumu, 83-92.

Özgenç, Ý. 1982. Kýzýlcaören köyü (Beylikahýr- Eskiþe-hir) fluorit- barit- bastneazit yataðýnýn jenetik

incelemesi. Ege Üniversitesi Yerbilimleri Fakül-tesi, Doçentlik tezi. 83 s.

Preinfalk, K.,Y. and Morteani, G. 2002. The pegmatitesof the Nova Era-Itabira-Ferros pegmatite distict and the emerald mineralisation of Capoerianaand Belmont (Minas Gerais, Brazil): geoche-mistry and Rb-Sr dating. Journal of South Ame-rican Earth Sciences, 14, 867-887.

Romieux, J. 1942. Sivrihisar, Paþa daðlarý ve Emir-daðlarý bölgelerinin jeolojisi hakkýnda rapor.Maden Tetkik Arama Genel Müdürlüðü Report No:1431, Ankara (unpublished).

Warner, L.A., Holser, W.T., Wilmorth, V.R. and Came-ron, E.N. 1959. Occurence of nonpegmatiteberyllium in the United States. U.S. Geol.Survey Prof. Paper 318, 198s.

Weingart, W. 1954. 56/2, 56/4 Sivrihisar ve 57/1, 57/3Ankara paftalarýnýn jeoloji haritasý hakkýndarapor. Maden Tetkik Arama Genel MüdürlüðüReport No: 2248, Ankara (unpublished).

40

PLATES

PLATE I

Figure 1- Garnet glaucophane schist (H1)Garnet (gr) indicating chloritization at its environs, and glaucophane (gl).Single nicole, Obx Ok= 5x10

Figure 2- Epidotite (H7)Epidote (ep) and calcite Double nicole, Obx Ok= 10x10

Figure 3- Chlorite lawsonite schist (H9) Chlorite (kl) with foliated crystals, and short prismatic crystals of lawsonite(lv), Double nicole, Obx Ok= 5x10

Figure 4- Karaburunsivri phonolite (H18) Hornblende (hnb), sanidine (sa) and leucite (lö) Double nicole, Obx Ok= 4x10

Figure 5- Kocasivri phonolite (H28) Hornblende (hnb) and sanidine (sa) minerals Single nicole, Obx Ok= 4x10

Figure 6- Pegmatite (H29) Baveno and Carsbad twins on orthoclase are seen. Double nicole, Obx Ok= 5x10


PLATE - I

1 2

3 4

5 6

PLATE II

Figure 1- Stereomicroscobic view of the crystals of aquamarine (A) at the left, emerald (Z)at the right, enlargement = 35X

Figure 2- Emerald photo taken by stereomicroskobic view, enlargement = 35x

Figure 3- View of a beryl grain in a 1.60-immersion fluid

Figure 4- Emerald at single nicole, Obx Ok= 5x8

Figure 5- Basal cleavage (0001) on aquamarine is seen. Single nicole, Obx Ok= 5x8


PLATE - II

1 2

3 4

5

PLATE III

Figure 1- General view of beryl crystals

Figure 2- Surficial view of a hexagonal prismatic beryl crystal (0001)


PLATE - III

1

2

INTRODUCTION

Although several types of serpentine mineralsare found in the nature, the most common onesare lizardite, chrysotile and antigorite. Theseminerals have the general formula ofMg3Si2O5(OH)4 and are described as triocta-hedric (1:1) layered silicates with MgO, SiO2 andH2O contents between 85-95%.

Serpentine minerals are formed as a result ofhydration of olivine, pyroxene and other Mg-richsilicate minerals under suitable conditions, theprocess so called serpentinization. Lizardite andchrysotile are formed at lower conditions ofgreenschist facies while antigorite mostly occursat greenschist-amphibolite facies (Evans, 1977).

In studies conducted on serpentine minerals,minerals are generally described by petrographi-cal methods and X-ray analyses and their for-mation conditions are determined and thus therock formation processes are investigated (Gür-

tekin, 2001). Hydrated oceanic crust material iscomposed of more than 90% of serpentine min-erals. During the subduction process, thermalreactions on serpentine minerals cause waterrelease which can play an important role in sub-duction-related volcanic processes. Completelyserpentinized peridotites contain significantamount of water (13%) which released as aresult of subduction process this water can betransported to great depth which is representedby high temperature-high pressure conditions atwhich serpentine minerals can be stable and arcmagmatism starts. Therefore, thermal reactionsof serpentines and related mineralogical chan-ges are very important for identification of somegeologic processes.

The aim of this study is to describe serpentineminerals on the basis of petrographic, X-ray andDTA-TG methods, to investigate the mineralogi-cal changes occurring during the thermal reac-tions and to determine the stability of antigoriteunder constant pressure. Samples used in the

THERMAL REACTION OF ANTIGORITE: A XRD, DTA-TG WORK

Gökçe GÜRTEKÝN* and Mustafa ALBAYRAK*

ABSTRACT.- It is very important to determine the stability limits of serpentine minerals for investigation of geo-logic processes taking place in the oceanic lithosphere which consists of serpentinized peridotites. As a result oftemperature increase in the subducting oceanic lithosphere, thermal decomposition of serpentine minerals andnew mineral formations have a great effect on geologic processes related to subducting plate. In this study, ser-pentine minerals (antigorite) collected from the Konya-Çayýrbaðý region were dehydrated under constant atmos-pheric pressure, then mineralogical changes were determined by using X-Ray diffraction and DTA-TG analysesand finally the stability limits of antigorite was determined. Dehydration reactions on antigorite started at approx-imately 100-150°C, dehydroxilation reactions started at approximately 550°C and beyond this temperatureforsterite started to crystallize from antigorite+brucite. Association of antigorite+forsterite continued until 650°C atwhich enstatite started to be formed. During all the reactions, which were carried out at the atmospheric pressure,talc was not formed but some H2O and amorphous silica were released. Dehydroxilation reaction on antigoriteoccurred between 550°C and 690°C and antigorite was stable until 650°C-690°C.

Keywords: XRD, DTA-TG, Antigorite, Dehydration, Dehydroxilation

* Maden Tektik ve Arama Genel Müdürlüðü, Maden Analizleri ve Teknolojisi Dairesi Baþkanlýðý, Ankara.E-mail: [email protected]

Mineral Res. Exp., Bull., 133, 41-49, 2006

Gökçe GÜRTEKÝN and Mustafa ALBAYRAK

study were taken from the Çayýrbaðý ophiolite inthe Çayýrbaðý-Hatip region in Konya (Figure 1)and serpantinites in the Hatip ophiolitic complex(Özcan et al., 1990).

THERMAL REACTION OF SERPENTINEMINERALS

Loosing of the absorbed water (H2O) relatedto the increasing of heat in a mineral is described

as dehydration and loss of water in its crystalstructure is descbried as dehydroxilation. Pro-cess of thermal reactions in serpentine (dehydra-tion and dehydroxilation) and forming of olivine+pyroxene+talc+chlorite, that minerals include afew or no water is described a deserpentinization(O'Hanley, 1996). Because, lizardite is firstlyformed from olivine during serpentinization, indeserpentinization olivine mostly formed fromantigorite and lizardite in deserpentinization.

42

Figure 1- Geological and location maps of the study area (Revised fron Özcan et al., 1986)

In general, thermal reactions in antigorite du-ring recessing serpentinization are in the form ofantigorite + brucite olivine + H2O orantigorite

olivine ± talc + H2O and new minerals are for-med at temperatures about 500-690°C (Evans,1977). Considering the stability boundaries ofserpentine minerals (Figure 2), lizardite andchrysotile are found at lower conditions of green-schist facies while antigorite is stable over a widerange from lower green-schist to amphibolitefacies.

MATERIAL AND METHOD

This work was conducted as two stages:X-ray analyses and DTA-TG analyses. However,prior to X-ray and DTA-TG analyses, petrograph-ical studies were carried out to determine textur-al characteristics, mineral paragenesis and sour-ce rock types of serpentinites. In petrographicalstudies, mineral paragenesis and textural proper-ties of rocks were described and classificationsof Wicks and Whittaker (1977) which were laterdeveloped by O'Hanley (1991, 1996) were used.

X-ray analyses of 5 samples from the studyarea were made with Rigaku Geigerflex brand X-

ray diffractometer at the MTA General Directora-te. Samples were thermally treated at constantpressure at the laboratory and the resulting min-eralogical changes were determined with the X-ray analyses. Since the main peaks have veryclose values, secondary peaks are very impor-tant for evaluation of serpentine minerals andtherefore, analyses were conducted at 2 =0-70º.Following the routine analyses performed atambient conditions, powdered samples were firstmixed with pure water and taken into suspensionthen they were dried on glass lamellas. Beforethe X-ray analyses, dried samples were left infurnace for about one hour at temperatures of200°C, 400°C, 500°C, 550°C, 600°C, 650°C,700°C, 800°C, 900°C, 1000°C and 1100°C. Inorder to prevent melting of glass lamellas, porce-lain containers were used for heating processesat 900°C, 1000°C and 1100°C.

DTA-TG analyses, which give information onphase transformations in parallel to temperatureincrease and the amount of mass loss, were per-formed with Rigaku Thermoflex TG 8110 branddevice at the MTA General Directorate. Duringthe analyses which were conducted at tempera-tures between 18.7°C and 1100°C, temperatureincreasement were selected as 20°C/minute and100 mg sample was used for the analyses.

Petrography

In petrographical studies, source rock of ser-pentines was found as harzburgite. In complete-ly serpentinized rocks with pseudomorphic tex-ture, serpentine±talc±magnetite mineral parage-nesis is observed but olivine (forsterite) andorthopyroxene (enstatite) minerals are absentand serpentinized (bastitized) orthopyroxene re-licts showing plastic deformation signs were alsodetected. According to classification of Wicksand Whittaker (1977) and O'Hanley (1991, 1996)on the basis of textural features under micro-scope, antigorite±lizardite and vein-type chryso-tile were found in samples of pseudomorphic tex-ture.

THERMAL REACTION OF ANTIGORITE 43

100

1

3

5

7

9

200 300

11

13

400

15

500

550450350260

600

670

700 800

Antophyllite

Antigorite

Antigorite

Forsterite

Forsterite

Enstatite

Brucite

Antigorite

Talc

AntigoriteChrysotile

Lizardite

Talc

Talc

Forsterite Antophyllite

Forsterite

Forsterite + Enstatite

Greenschist Amphibolite

P (kbar)

T (C )O

Figure 2- Stability limits of serpentine minerals (Buc-ker and Frey, 1994)


X-Ray Analyses (XRD)

In order to determine mineralogical changesas a result of thermal reactions, samples thatwere heated at certain temperature were subject-ed to X-ray analyses. For easily determination ofmineralogical changes, block diagrams preparedusing the Jade program that show the results ofanalyses at various temperatures were present-ed in figures 3, 4, 5, 6 and 7.

Results of routine analyses are conformablewith those of petrographic studies and antigoritewas the main mineral observed. However, due toits lower abundance (2-3%), chrysotile could notbe detected in X-ray analyses. There was nomineralogical change in analyses of all samplesconducted at 200°C, 400°C and 500°C while onlya little decrease was observed in the antigoriteabundance with temperature increase. It wasobserved that the antigorite abundance was con-tinued to decrease at 550°C and olivine(forsterite) started to crystallize. At 600°C, antig-orite abundance was significantly decreased andforsterite continued to crystallize and its abun-dance was increased. At 650°C, antigorite wasmostly disappeared and forsterite continued tocrystallize and enstatite was started to appear. Inanalyses performed at temperatures higher than700°C, forsterite and enstatite continued to crys-tallize and their abundances were increased.Considering the analyses conducted at 550°C,600°C and 650°C, a significant amorphousiza-tion was detected in samples 11S and 29A(Figure 8).

DTA-TG Analyses

According to results of DTA analyses, sam-ples 1 and 29A yielded endothermic and exother-mic peaks at 695°C and 810°C, respectively.Samples 6, 11B and 11S also showed similarfeatures with three endothermic peaks at 210°C,380°C and 690°C and, one exothermic peak at810°C (Figures 9, 10, 11, 12 and 13).

44

Figure 3- XRD block diagram of sample 1. The numbers 1: Dried, 2:200°C, 3:400 °C, 4:500°C,5:550°C, 6:600°C, 7:650°C, 8:700°C,9:800°C, 10:900°C, 11:1000°C, 12:1100°Cshow the XRD analyses at that temperatu-res. (atg: antigorite, fo: forsterite, ens:enstatite)

Figure 4- XRD block diagram of sample 6. The num-bers 1: Dried, 2:200°C, 3:400 °C, 4:500°C,5:550°C, 6:600°C, 7:650°C, 8:700°C,9:800°C, 10:900°C, 11:1000°C, 12:1100°Cshow the XRD analyses at that temperatu-res. (atg: antigorite, fo: forsterite, ens:enstatite)

Figure 5- XRD block diagram of sample 11B. The num-bers 1: Dried, 2:200°C, 3:400 °C, 4:500°C,5:550°C, 6:600°C, 7:650°C, 8:700°C,9:800°C, 10:900°C, 11:1000°C, 12:1100°Cshow the XRD analyses at that temperatu-res. (atg: antigorite, fo: forsterite, ens:enstatite)

THERMAL REACTION OF ANTIGORITE

Thermal reactions in antigorite are developedin parallel to temperature increase and at a tem-perature of 100°C, free water in samples and ab-sorbed water on the surface are lost due to dehy-dration. Examination of DTA and TG curves re-veals that there is such a change in all samplesat 100°C. Endothermic peaks at 210°C and380°C for samples 6, 11B and 11S are attributedto clay minerals and brucite within the serpentineminerals that could not be detected in X-rayanalyses due to their lower abundance. Accor-ding to McKenzie (1970), montmorillonite groupclay minerals give two endothermic peaks at125-260°C and 625-750°C temperature range

while brucite gives only one endothermic peak at356-455°C temperature range. Examination ofDTA diagrams yields endothermic peaks of clayminerals at about 210°C and of brucite at 380°C.The endothermic peak expected for the clay min-erals at temperatures between 625°C and 750°Ccoincides with that of antigorite.

Antigorite peaks in all samples are observedas endothermic at 690°C and exothermic at810°C. As shown in DTA curves, dehydroxilationwas occurred at about 550°C to 690°C. As deter-mined by the X-ray analyses, reactions associ-ated with dehydroxilation resulted in formation offorsterite from antigorite (Mg3Si2O5(OH)4) at tem-peratures above 550°C and enstatite (MgSiO3) attemperatures above 650°C. In XRD analyses,antigorite was lastly found at 650°C and consid-ering the results of both DTA and XRD analysesreveal that antigorite can be stable at tempera-tures mostly 650°C-690°C. At temperatures high-er than 690°C which defines the upper stabilitylimit of antigorite, forsterite and enstatite contin-ued to crystallize and this new mineral formationwas recorded on DTA diagrams as two exother-mic peaks at around 810°C. As a result, all thesemineralogical changes determined with the XRDstudies are found to be conformable with DTAanalyses.

According to results of TG analyses, 11%mass decrease was found in all samples (Figu-res 9, 10, 11, 12 and 13).

RESULTS AND DISCUSSION

Water plays an important role in formation ofvarious geological processes. Serpentinizedoceanic lithosphere is believed to be the sourceof water that is effective in development of sub-duction-related calc-alkaline arc volcanism (Ul-mer and Trommsdorf, 1995). In this respect, sta-bilities of serpentine minerals are very importantfor determination of mode of occurrence anddepth of these processes. Therefore, thermalreactions of serpentine minerals and mineralogi-

45

Figure 6-XRD block diagram of sample 11S. The num-bers 1: Dried, 2:200°C, 3:400 °C, 4:500°C,5:550°C, 6:600°C, 7:650°C, 8:700°C,9:800°C, 10:900°C, 11:1000°C, 12:1100°Cshow the XRD analyses at that temperatu-res. (atg: antigorite, fo: forsterite, ens:enstatite)

Figure 7-XRD block diagram of sample 29A. The num-bers 1: Dried, 2:200°C, 3:400 °C, 4:500°C,5:550°C, 6:600°C, 7:650°C, 8:700°C,9:800°C, 10:900°C, 11:1000°C, 12:1100°Cshow the XRD analyses at that temperatu-res. (atg: antigorite, fo: forsterite, ens:enstatite)


cal changes occurring during these events areprimarily important.

A number of experimental works were con-ducted for determination of stabilities of serpen-tine minerals (Wunder and Schreyer, 1997) (Fi-gure 14). In this study, serpentine minerals weresubjected to thermal treatment to investigate theupper stability limits of these minerals and result-ing new mineral paragenesis. In this study antig-orite was used which is more stable in compari-son to other serpentine minerals and, it wasdetermined that different mineral paragenesiswere obtained under various pressure and tem-perature conditions. Wunder and Schreyer(1997) compiled results of previous works (Figu-re 14) and determined the stability limits of antig-orite and following reactions were stated to betaken place during dehydroxilation of antigorite:

Antigorite talc + forsterite + H2O(15 kbar, 640 °C) (1)

Antigorite forsterite + clinoenstatite + H2O (77 kbar, 680 °C) (2)

Antigorite clinoenstatite + brucite + H20(>77 kbar, >680 °C) (3)

According to Ulmer and Trommsdorf (1995),forsterite is formed by the reaction between an-tigorite and brucite (if available) at low tempera-tures (antigorite + brucite forsterite + H2O)and about 3.5% H2O is released. With furtherincrease of pressure and temperature, brucite iscompletely removed and as shown in reactions 4and 5, different minerals are formed. Diagramshowing the stability limits of antigorite is shownin figure 15.

Antigorite forsterite + talc + H2O(low pressure) (4)

Antigorite forsterite + enstatite + H2O (high pressure) (5)

In this study, antigorite minerals were subject-ed to thermal treatment under constant pressure(laboratory conditions). Mineralogical changesoccurred during this process were determinedwith XRD and DTA-TG analyses and stability lim-its of antigorite were determined under constantatmosphere pressure.

All the samples are mostly composed ofantigorite. However, on the basis of DTA analy-ses results, little amount of montmorillonite andbrucite were also found in samples 6,11B and11S.

46

Figure 8- The amorphousization at 600°C (Sample 29A, Atg: antigorite, Fo: Forsterite)


Considering the results of XRD analyses, an-tigorite can be stable until a temperature range of650°C-690°C but its abundance decreasesdepending on reactions associated with temper-ature increase. Increase in antigorite abundancewas determined from peak intensities on XRDcharts. In analyses at temperatures above550°C, the amount of antigorite was furtherdecreased and forsterite started to be formed.Antigorit+forsterite association at temperaturesabove 550°C was continued until 650-690°C andantigorite was removed at higher temperatures.Results of DTA analyses which were conforma-ble with X-ray determinations indicated that

47

Figure 9- DTA-TG curves of sample 1

Figure 10- DTA-TG curves of sample 6

Figure 11- DTA-TG curves of sample 11B

Figure 12- DTA-TG curves of sample 11S

Figure 13- DTA-TG curves of sample 29A


antigorite dehydroxilation reactions were startedat 550°C and continued until 690°C.

X-ray analyses conducted at temperaturesabove 650°C reveal that in addition to forsterite,enstatite also occurs and abundance of bothminerals increases with temperature increase.According to results of DTA analyses , endother-mic peak shown at 810°C following the dehyd-roxilation at 690°C correspond to formation offorsterite and enstatite. However, XRD resultsimply that enstatite forms in a later stage thanforsterite (after 650°C).

In samples 6, 11B and 11S, antigorite isaccompanied by little amount of brucite and, as a

result of their reaction forsterite is formed andsome amount of water is released. In brucite-freesamples (e.g., 1 and 29A), forsterite is formedfrom antigorite and similarly some amount ofwater is released. Examination of XRD analysesconducted at 550°C, 600°C and 650°C reveal thepresence of amorphousization that is observed inall samples but particularly significant in samplesnos. 1 and 29A. The amorphousization is thoughtto be derived from silica that is released duringthe thermal reactions. Considering this, followingreactions were first occurred during thermal reac-tion of antigorite:

Antigorite + brucite forsterite + H2O + SiO2

(550°C-650°C) (6)

Antigorite forsterite + H2O + SiO2

(550°C-650°C) (7)

According to results of XRD analyses, duringthermal reaction of antigorite enstatite is formed

48

Figure 14- Previous experimental study of stabilitylimit of serpentine minerals (Wunder veSchreyer, 1997)

Figure 15- Stability limit of antigorite (Ulmer veTrommsdorf, 1995)


following the forsterite (650°C) and followingreactions took place during the formation ofenstatite:

Antigorite forsterite + enstatite + H2O (650°C-690°C) (8)

Forsterite + SiO2 enstatite (>650°C) (9)

As a result of dehydroxilation reactions occur-ring between 550-690°C it was found that firstforsterite forms antigorite. The amorphousizationthat was determined by XRD analyses andobserved in between dehydration and crystalliza-tion reactions may indicate that in addition towater some amount of silica was also releasedduring these reactions. At temperature above650°C forsterite is accompanied by enstatite.

Considering all these data, antigorite wasfound to be stable up to temperatures about 650to 690°C. During dehydroxilation, antigorite-forsterite association was observed at tempera-tures above 550°C and enstatite starts to crystal-lize above 650°C. Forsterite+enstatite associa-tion is dominant by 690°C.

ACKNOWLEDGMENTS

Authors are grateful to the staff of Mineralogy-Petrography section of MAT Department of theMTA General Directorate for providing laboratoryassistance. Appreciation is extended to Dr.Kývanç Zorlu (Mersin University, GeologicalEngineering Department) for his contributions.

Manuscript received on January 25, 2006

REFERENCES

Bucher, K. and Frey, M. 1994, Petrogenesis of Me-tamorphic Rocks, sixth Edition, 318 pp.

Evans, B.W. 1977 Metamorphism of Alpine peri-dotites and serpentinites, Annual Review EarthPlanetary Science, 5, 397-448

Gürtekin, G. 2001 Mineralization stages of serpen-tinites in Çayýrbaðý (Konya) Ophiolites, Hacet-tepe University The Institute for GraduateStudies in Science and Engineering, M.Sc.Thesis, 93 page (unpublished)

McKenzie, R. C. 1970 Differential Thermal Analysis,Volume 1, Fundamental Aspects, AcademicPress Inc. (London) LTD. 775 pp.

O'Hanley, D.S. 1991 Fault-Related phenomena asso-ciated with hydration and serpentine recrystal-lization during serpentinization, Canadian Mi-neralogist, 29, 21-35

O'Hanley D. S. 1996 Serpentinites-Records of Tec-tonic and Petrological History, Oxford Mono-graphs on Geology and Geophysics No.34

Özcan, A., Göncüoðlu, M. C., Turhan, N., Þentürk, K.C. and Uysal, Þ. 1986 Geology map of theKonya-Altýnekin-Kadýnhaný ve Ilgýn Regions, MTA Map.

Özcan, A., Göncüoðlu, M. C., Turhan, N., Þentürk, K. C. and Uysal, Þ. 1990 Geology of the Konya-Altýnekin-Kadýnhaný ve Ilgýn Regions, MTAReport No: 9535 (unpublished).

Ulmmer, P. and Trommsdorff, V. 1995 Serpentine sta-bility to mantle depths and subduction-related magmatism, Science, 268, 858-861

Wicks, F.J. and Whittaker, E.J.W. 1977 Serpentinetextures and serpentinization, Canadian Mine-ralogist, 15, 459-488

Wunder, B. and Schreyer, W. 1997 Antigorite: High-pressure stability in the system MgO-SiO2-H2O(MSH), Lithos, 41, 213-227

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